I'm caught a bit off guard by David Cameron's opening remark. He's standing under the destination board at Liverpool Street station, mobile clamped to his ear, clutching a file of papers. A woman nearby is staring at him, intently and obliquely, from behind her fringe. She perhaps knows who he is, but among all the people milling about and hurrying past, no one else seems to give a second glance to the tall, well-scrubbed-looking chap in the dark blue suit - Paul Smith, he later tells me - who looks as though he might be on his way to work in a bank, or to some business meeting. Then he finishes his call. I go over, introduce myself, say hello. "D'you think that's Bobby Robson?" he asks.
With a discreet jerk of his head he signals to look behind him. There, in a similar dark suit and clutching a similar file of papers, is a craggy-looking man with a shock of grey hair. Though this is the very last thing I'm expecting on first meeting a possible future Prime Minister, we engage in a murmured debate as to whether this is indeed the one-time England manager, or a lookalike. We have just decided it's a lookalike when a passer-by proves us wrong by going up to him and elaborately shaking his hand.
Though Cameron has been on TV for weeks, in the "Station Concourse Celebrity Recognition Challenge" football is still ahead of politics: current score 1-0. In a funny way, this could even be to the Conservative Party's advantage.
That is because now, for a change, the party's 254,000 members have the chance to elect a leader who barely merits a second glance at Liverpool Street - because he seems just like the rest of us. He doesn't look like someone's dotty old Dad, or frankly a bit weird - not like John Major, with his owlish manner and outsize specs; or William Hague, baby-faced but shiny pated, with his strange "Churchill goes to Yorkshire" accent; or Michael Howard with his peculiar way of saying "peoplllle" as if it had half a dozen "l's in it. People in politics will dismiss such trivial reasoning as beneath contempt and insist that what matter are issues and policies and plans for tax and pensions. But everyone else knows that, for a huge swathe of the electorate, choosing who to vote for - in an election or in a leadership contest - is largely an emotional decision, about who they think they like. As one elegantly tweedy Tory party member in pearls tells me later that day, out in the shires: "They've either got to make your heart melt - or you think: "Oh no, have we got to put up with him?". But this time, she adds, she is agonising over her ballot paper: Cameron and Davis are neck-and-neck in her heart-melting test.
They both seem like the sort of person you could have a chat with if you bumped into them in the pub. With his boxer's nose and silver hair, David Davis calls to mind a football club boss, who'd be able to tell you some decent jokes. David Cameron, who wants an iPod for Christmas and takes his kids swimming on Saturday mornings, comes across as an ordinary young Dad. Whichever of them leads the party into the next general election (and Cameron is heavily odds-on with the bookmakers), this emotional appeal may well prove more important than the minutiae of economic strategy in attracting new, uncommitted voters in large numbers.
With their good-naturedly bloke-ish style in the head to head debates - "After you David." "No, after you David" - both men have been urgently repainting the Conservative Party to try to give it a human face. Cameron, in particular, has being doing so with such enthusiasm that some are now daring to hope that, if he becomes leader, all this might - just might - work, and miraculously revive the corpse. Among the faithful, there are suddenly real, whispered hopes that the next election could even - who'd have thought it? - be winnable.
Today Cameron is taking his vision of a "modern, compassionate Conservatism" to Norwich. I'd expected a team of minders and advisers in crisp suits, barking into mobile phones like in The West Wing, but there's just him and his press officer, Gabrielle Bertin, elegantly panicking that the snail-like ticket queues may cause us to miss the train altogether. But Cameron stays calm. It's been a bewilderingly gruelling leadership campaign and there must have been many moments like this.
Finally, jacket off, he settles into his seat, apologising as he stifles a yawn. At this point last week, he and David Davis are midway through the series of 11 hustings around the country. It's trains, planes, helicopters, and a diary so crammed that it barely leaves time for anything except speeches and interviews. The previous day he'd been in Scotland and got home close to midnight.
"It's tougher than I expected in some ways," he says. "I mean, it's very like a sort of general election campaign: every day you're going to a new part of the country, big meetings; you know, yesterday - 400 people in Ayr, a group of businessmen in Edinburgh, 650 people at the hustings in Perth, three newspaper interviews, two television interviews, two radio interviews - by the time you've done all that you feel quite whacked. I got back at about sort of half past 11 or something last night, but then I always have to sit down and sort of chill - you can't go straight to bed. So I ended up watching Jonathan Ross's film programme, which was quite a good way of winding down."
Today he's been up since 6.45am, got his disabled son Ivan ready for school, flicked through the papers, worked on a speech, and now it's more of the same: a morale-raising vote-for-me pitch to party members in Norwich, a blizzard of soundbite interviews, helicopter to Cambridge, another hustings, more interviews, endless calls on his mobile. And unless the polls and the gossip and the feedback from the constituencies are catastrophically awry, Cameron will, on Tuesday, be announced as the next leader of the Conservative Party, with a fighting chance of becoming a future Prime Minister. A few months ago, almost no-one outside the Westminster loop had heard of him. Is even he a bit surprised to find himself here?
"Yes, in many ways," he smiles. "But in another way no, because after the election I thought long and hard about whether or not to stand. And I came to the conclusion it was the right thing to do because I knew what needed to be changed in the Conservative party, and what the big challenges are facing the country; and when I launched the campaign and started getting it moving, I always thought there was a chance - a good chance - of winning. I wouldn't have done it otherwise. And the people around me thought I could win. And there weren't many of us to begin with," he adds with a smile. He often jokes that at the outset the Cameron supporters group was such an exclusive club they could all have fitted into the back of a cab. These "people around me" have been tagged by commentators as the "Notting Hill set", a group of fiercely bright Tory Young Turks, mostly ex-Oxford, many of whom are graduates of the Conservative Research Department, which serves as a kind of finishing-school-cum-training-ground for the party's ambitious young hopefuls. The network of connections extends from Westminster via the elegant white stuccoed townhouses of Notting Hill out to the Old Rectories and market towns of the Home Counties, and back to a previous generation of landed gentry and Tory MPs. But a Cameron team member is keen to dismiss the idea of a "Notting Hill set" as largely a figment of the media's imagination.
"The truth about it," he says, "is there is group of people there which includes people like Steve Hilton [former ad-man, the campaign's creative brains], and David [Cameron], and George [Osborne, shadow chancellor and campaign manager] who all knew each other during their days in the early 1990s when they were all in the Conservative Research Department together; they went off to do their own things in the private sector, and a lot of them have now returned to politics. They're friends, they've known each other for a long time, they trust each other: but if you think they move like some cohesive force, like a clique, they don't really."
Whatever, it's this so-called new "Notting Hill" generation of young modernisers (some of whom have social links with their Millbank counterparts from New Labour) who now look likely to win control of the party. Among its key members beside Cameron and Osborne are Oliver Letwin; Michael Gove, the columnist and MP for Surrey Heath; and another Conservative Research Department former staffer, Ed Vaizey, MP for Wantage (a stone's throw from David Cameron's own Oxfordshire constituency of Witney).
It has been alleged that after the general election result, when Michael Howard announced he was to stand down, the group decided that, out of them all, Cameron had the best chance of becoming leader, and that he was persuaded - fairly robustly, according to one report - to stand. An unnamed MP is said to have telephoned Cameron the weekend after Michael Howard's resignation announcement, saying: "Sorry David, I'm afraid you've got to stand."
Cameron is a little bashful about this. "No, that is not quite... that is not really true," he says. "I mean there was a group of us who I think shared the same analysis of what the party needed to do, but the decision was very much one that I came to after having listened to people, and thought it through, and I talked to my wife and other people in my family - and I can't point to one sort of epiphanal moment striding across the Cotswolds when I thought: 'This is my destiny.' I just increasingly thought this was the right thing to do. And having the support of people like Oliver Letwin was important. If I couldn't have got the support of people like him and George [Osborne] and others, I don't think it would have been a runner, because politics is about building a team around you."
He also claims that there's no basis in reports that there was a Granita-style deal between him and Osborne done over a meal at Zucca, on Notting Hill's Westbourne Grove, over which of them would stand. "No, no," he says. "The thing about George and I is we don't have one-off epoch-making dinners. We bicycle to work together, we're great friends, I'm godfather to his daughter, and we talk about these things all the time. And so there's no pact, no deal, no Granita. We're friends and colleagues, and he's been incredibly supportive and unbelievably helpful, and very good campaign manager. He's just a very good thinker about politics and has a very clear view about what needs to be done. That's been very helpful in forming my own view."
With the relaxed self-assurance which an education at Eton and Oxford seems often to afford, Cameron appears remarkably at ease with the prospect of becoming party leader, despite the pressure and the mauling he must expect from Labour - and the fact that he and his wife Samantha have two young children (one of whom, Ivan - who's nearly four and suffers from cerebral palsy and severe epilepsy - requires round-the-clock care). And they are trying to move house in London. And they have a baby due in February.
He accepts that the prospect is daunting. "Of course it is - everything in politics is daunting. The more you try to do, the more daunting it becomes. I thought through very clearly before deciding to stand. It was not 'shall I stand?' it was 'will I be able to handle it if I win?' That was the decision I needed to make - because all of this is hard work and gruelling, but it's nothing compared with the pressure of the three-and-a-half years before the next election.
"But I still think - and I hope this isn't naïve - that you can do a job like that [and still have] a family life, because I think that's important. It's the going home at night, and switching off, and dealing with things at home that helps you be balanced and reasonable and make good decisions the next day. So that's my determination, to try to keep some semblance of normal life."
Opposition, he says, "is about judgement more than anything else - it's about the strategic direction for the party, where you want it to be, where to oppose the government and where to say they've got it right and back them (he calls this "consistent Conservatism") and then lots of judgement about people and teams and all of that. That's what you've got to get right - the big decisions, not the little stuff."
He's blithely unconcerned by repeated criticism that he's light on policies [see box overleaf], and that no-one knows what they are - in contrast, for example, to David Davis's robust promise of £38bn in tax cuts.
"The key thing," says Cameron, "is getting the right judgement between the clear direction you want to set but without nailing your every last policy down, which would be absurd, after three general election defeats, in a six-week campaign. So I'm very unruffled by these accusations of lack of substance on policy, because I think if you actually look at all the things I've said, there's buckets of substance - but hopefully not too much.
"And I'm discovering this in politics: people have to have something to throw at you. For a while it was the Eton thing, and then it was the drugs thing, and now it's the substance thing - as it were," he adds. "And you just have to make the right judgement on each one as you see it, and then stick to your guns."
He has done just that on the drugs question (whether he had taken Class A drugs or not) which, perhaps against the odds, has all but faded away in the face of his resolute insistence that everyone - even a possible future Prime Minister - should be entitled to a private past which should remain private. On this, Tory-supporting Fleet Street clumsily executed a classic U-turn. Having at first depicted him as an insubstantial lightweight with a possibly dodgy past, they then, in the face of no evidence and positive polls, were forced into urgently redrawing him as the bright young salvation for the party. Once it became clear that Cameron was hot favourite to win, they didn't have much choice; no one wants to be seen to have backed the wrong horse.
Had this drugs question been the biggest crisis of the campaign? "I've been challenged and tested in a number of ways - and none of them has been life-threatening," Cameron replies. "I thought I drew a perfectly sensible distinction between your past that can remain private, and your current life - and it took a bit of time to get that across to people, but I think generally at the end of that process the opinion polls seemed to back me. You feel a bit at the centre of a storm because of the newspapers, and you sort of feel a bit..." He tails off. "But there were no sleepless nights."
This was an issue which, depending on how it was handled, could clearly have spelt life or death for his candidacy - and thus make or break the career prospects of his supporters. But he insists that he was not advised to adopt this stance by his campaign staff. "No, it was very much my own view - funnily enough. And there were plenty of people telling me it was not the right view. But it was very much my own, and I think the Question Time I did proved to people that this is a perfectly reasonable distinction, and one that is actually supported by a lot of people in the country."
Has the issue come up at the hustings? "Yeees... The drugs question has come up, more about policy than personal - er - stuff," he says. "But it comes up from time to time and I get questioned about it and I'm very comfortable with that because I think I've drawn a reasonable distinction."
Reports from party members who have attended these closed hustings have several times referred to both candidates saying to each other, "I agree with everything David has just said." But Cameron insists that there is indeed clear water between him and Davis, and that this election is not merely a beauty contest.
"Obviously we agree about lots of things; we're Conservatives, we've been in shadow cabinets together and so on," he says. "But I think there's a choice on a number of levels. And there's an attitudinal difference between us. David has said: "We lent power to Labour in 1997; we want it back again..." I have a totally different attitude, in that we haven't lent power to anyone. We lost the election. We have to win back the trust of people. That's a huge mountain to climb. I think his appeal is much more about having similar policies, and shouting about them louder, if I can put it like that. He wants to have big upfront tax cuts; I want to have a clear direction but no promises about tax that we can't afford. I want to scrap the opt-out policy on the NHS, because I think it takes money out of the NHS. He wants to still have it. So there are differences. I think it would be wrong to characterise it entirely as 'change versus more of the same', but there is an element of that."
Today, at this point in the campaign, 117 of the 198 Conservative MPs had declared their support for Cameron. "I think there is now a consensus for change in the party," he claims. Could this also include a change of name for the party?
"Some people have suggested adding a word, but I don't think it's actually the answer. I mean, look at Tesco - that used to be the cheap crappy supermarket, and over time it's transformed itself, and it didn't change its name."
He says it's about making "subtle changes" rather than "some sort of rebranding or renaming exercise". The difficulty, he says, is that the party has no one policy whose abandonment could transform it at a stroke - such as Labour's dumping of "Clause 4" (its commitment to nationalisation).
"It's a more subtle process. Firstly, it's about making sure the party reflects the country; which is about the representation of women, and appealing to young people, and getting back into the cities. Secondly, it's expanding the policy portfolio to encompass things like climate change. And the third thing is all the key principles, and trying to explain what they mean today: that 'low taxes' doesn't mean tax cuts for the rich - it means keeping taxes down to have a competitive economy and jobs for all. So it is a more subtle process but it's already underway. With the influx of new MPs since the election, the move is in the right direction already." That all sounds fair enough. Or so far so woolly, depending on your point of view. And it still leaves 81 sceptical Tory MPs - 40 per cent of the total - who don't think it will work.
As the train draws into Ipswich, another passenger who's been sitting unnoticed at the other end of the compartment gets up and puts on his coat. He has a by now familiar shock of grey hair. "Is that who I think it is - David Cameron?" asks Sir Bobby Robson. (Latest score: football 1, politics 1.) On being assured that it is, he says he's going to say hello. "I thought it was you," he says to Cameron. "And I thought it was you," Cameron replies, as handshakes and best wishes are exchanged, along with a light-hearted enquiry from Cameron as to whether he's coming to Norwich to manage the Canaries. The answer's no of course, but Sir Bobby says it's very nice to meet him and wishes him luck.
"I'm a supporter of all politicians - of all parties," Sir Bobby confides mischievously as he's getting off the train. He's doing a book signing today in Ipswich, where he had a 14-year golden patch as manager in the 1970s and early 1980s (FA and Uefa Cup wins, and twice runners-up in the league). "This is my old stamping ground," he says, with a touch of pride. "What do I think of Cameron? He's a fine chap - and I wish him well in everything he does."
This celebrity interlude stands Cameron in good stead as an ice-breaker at the party meeting in Norwich's Georgian Assembly House, next to the Theatre Royal, where we arrive late after getting badly lost in the town's infernal one-way system. A Cameron-supporting MP from an outlying constituency is driving us to the meeting from the station, but even he doesn't know the way. Gabrielle's printed directions don't seem to match the street names we're passing. She's on her mobile to someone, desperately trying to get a fix on where we are. The MP is barking "Theatre Royal?" at people on the pavement, but they're mostly stumped. We drive round and round. Somewhere around here, there's a hall full of people waiting for us. The sense of desperation mounts.
But Cameron, sitting calmly in the front passenger seat, seems immune to this, as relaxed as if he were on a Sunday drive in the country. Spotting a street-sweeper up ahead, he winds down his window and enquires politely and without a hint of urgency as to the whereabouts of the elusive Theatre Royal. Up there, left at the T-junction - and within seconds of stepping on to the podium under the chandeliers in the Assembly House Music Room, Cameron has his audience of some 150 party members roaring with laughter. There's an apology about being "completely defeated" by the one-way system, and a "bad news" segment - Sir Bobby's not coming to manage the Canaries - and a remark that on any podium like this he always looks round expecting to see a Dimbleby. They're loving all this. Then he adds: "And I had... er... Jeremy Paxman last week. And I like to think I really had him." A deafening roar of approval rattles the chandeliers. Whether this is more because they like Cameron or loathe Paxman is hard to tell. Cynics might suspect the latter.
The warm-up over, he sets out his crowded stall here with passion and fluency, talking without notes. He conjures up a warm, fuzzy vision of a party of opportunity, aspiration, optimism and change, backed by his conviction that under a reworked Conservative government, Britain's "best days lie ahead". Summoning up the spirits of Margaret Thatcher and Winston Churchill, he says they, too, embodied the "forward-looking Conservatism" which, he insists, will help the party win power once more.
"That's why this is so important - we've lost three elections in a row. If we just have the same approach, the same policies, but shout a bit louder, we will get the same result again," he says. "If we lose again, we will have been out of power for 17 years." Change, he insists, is vital so that "our party reflects the country we want to govern". He mentions the women voters the party must attract. "We need to recognise that for many young women, particularly working women, the issue of childcare and the balance between work and family is not just one issue among many - it is for them the issue. And we need to address that."
To resuscitate the party in Britain's major cities - many of which he describes as "Conservative-free zones" - he talks of a new approach to urban regeneration; "setting the voluntary sector free" to deal with problems of family breakdown, drug dependency, high crime. "If we do that," he insists, perhaps somewhat optimistically, "we can win again in our cities."
He calls for more women MPs - there are currently 17 on the Conservative benches - "not because we are politically correct, but because we want to be politically effective. We need the conversation within the Conservative Party to be more like the conversation we want to have with the rest of the country."
And of the missing young supporters, he says: "Young people today have many of the values and principles and aspirations that we have. They want desperately to buy their first flat, to own their own home. They look at their wage packet, their payslip, and look at house prices - and they think: I'm not going to achieve that aspiration." He proposes more shared ownership schemes, more starter homes - and, in explanation of his perhaps controversial proposal that the party should support Labour "when they get things right", he says young people are "switched off" by the "Punch and Judy politics" of the House of Commons. He talks of climate change, poverty in Africa, the use of greener energy sources such as biomass - the things, he says, that young people care about. In a bold prediction (which would surely draw a withering look in any bookmakers), he adds: "I think if we have that sort of approach, young people who are idealistic, who share many of our values, will flock to us."
He talks of sharing the benefits of growth between tax cuts and public services, so that tax cuts aren't seen as "tax breaks for the rich"; about scrapping regional assemblies and other "regional" bodies, and giving power back to local organisations; about reforming the police, with elected, accountable commissioners; and of a "small state" which must be the servant, not the master, of the people.
"But when we roll back the state, we don't leave the poor, weak and vulnerable behind," he adds. "We help them by unleashing the voluntary sector in the way I explained. That's what I mean by modern compassionate conservatism. Modern, because we think our best days lie ahead. Compassionate, because we care about those who can get left behind. But Conservative, because it's those insights, principles and values that we share that will make this country even stronger."
This message of "modern, compassionate Conservatism" probably all sounds like sensible stuff in the airy living-rooms of Notting Hill, but how does it really play, in the country, to a predominantly elderly audience of core Tory faithful? Their concerns can be glimpsed in the question and answer session which follows his address.
Among questions from the floor: Is ultimate withdrawal from Europe possible or desirable? He says it's not a simple matter of being in Europe or out, but "we have given up too many powers to Europe and some of them are doing us great damage. To me the absolute imperative should be the return of the social and employment legislation and powers which are doing us so much harm."
Do you believe in capital punishment? He answers, "No. I think the danger of miscarriages of justice, of an innocent man being sent to the gallows, is just too great."
After nearly an hour, Cameron emerges to a scrum of local press, radio and TV interviews in the courtyard outside the Assembly House, before being driven off and helicoptered to more meetings, and on to that night's hustings near Cambridge. So, what do the party faithful think of it all? I pick a distinguished-looking couple at random. "To my mind he didn't come over as well as I thought he would," says one of them, Richard Colman. "David Davis came over much better than his image, and this chap came over worse than his image.
"But I'm still going to vote for him - he said the right things. But he didn't quite have what one imagined he was going to have. I thought he would be louder, and more positive. And we were sitting with four other people who have now heard both candidates, and they all said they'd vote for Davis."
He says he feels that the push to attract young voters is a non-starter. "I think it's a bit of a nonsense, because no one under 30 is interested in voting, are they? Our son's 30, and he voted for the first time in the last election. To worry about the young is, I think, a waste of effort."
Jennifer Colman feels unsettled by Cameron's youth. (He is 39.) "It's very difficult to define this, but you need a bit of oomph, and he's almost too young to have that," she says. "We saw David Davis the other day, and when he walked into the room everyone turned round and I thought: Oh, he looks better than his image. When you're comparing the two, I think Davis has more oomph. Obviously Cameron's young, and he's good-looking, but I think he needs a bit more maturity - that was William Hague's problem. We're going to fill in our ballots today - but it's difficult isn't it? I'm not quite certain. I'm going home to think about it."
In the past few weeks, thousands of party members will have done much the same, wrestling at kitchen tables across the country with these and other knotty questions - to which the answers are currently unknowable. Davis might seem a "safer" bet, but can he revive the party and pull in the new voters it so needs? As for Cameron, how much substance is there behind his feel-good message? Does he have the experience? Does he have that oomph? Is there a real leader behind the charm? In short, how much of him is real, and how much is presentation - or, as his detractors put it, "spin"?
Cameron's political CV might seem perilously brief for someone aspiring to high office (he's only been an MP since 2001). Critics have implied that he has risen without trace (an "all but unknown Old Etonian", as he was described last week). It could be argued - and is of course by Cameron - that neither charge is strictly true.
Born in London in 1966, he spent his first three years there before his family moved to an old rectory between Wantage and Newbury in Berkshire, where his parents, now in their 70s, still live. His father Ian is a former director of estate agents John D Wood and also of City stockbrokers Panmure Gordon, which, says Cameron, "was almost like a family firm. My father was there for 40 years, and my grandfather and my great grandfather too - they were all involved in the firm." His mother Mary furnishes the political lineage. Her grandfather Sir William Mount was MP for South Berkshire, a seat which he took over from his father, also William Mount. (Sir Ferdinand Mount, head of Margaret Thatcher's policy unit in the Eighties, is her cousin.)
Cameron recalls a "very happy childhood" with his brother Alec and sisters Tania and Clare ("I remember it being a very outdoors existence, walking, or shooting with an airgun, or tobogganing. It was a very happy home, with lots of friends.")
He was despatched to prep school, then Eton. He seems to have led a pretty blameless existence here, and his then headmaster Sir Eric Anderson recalls him as a "bright boy, and a nice one". Another master is said to be surprised at Cameron's rise. "You wouldn't have guessed it," he is reported as saying. "It's true with your boys that you are very often surprised by what they do. I wouldn't have had him marked out as a future leader'.
Cameron's a bit hazy on his O-levels ("they weren't very good - I think I got 12, but my maths was terrible - I think it was four As, three Bs, and five Cs or something like that. Does that make 12?"). But he achieved grade As in his history, history of art, and economics with politics A-levels. By the time he left Eton he was among the top-ranking tennis players at the college. ("I was quite good at it," he says modestly. "And I played a bit of cricket, but not very well.")
In 1985, he took a gap year, working initially in the offices of Sussex MP Tim Rathbone, and then in Hong Kong for three months for a shipping agency. He says he loved it. "I was 18 , a kind of junior office boy, and I had to go out by boat to meet all these Chinese, American, and Australian ships as they came in, and go through all the paperwork with them, the loading certificates and so on." He went on to Japan, crossed to Russia, then took the Trans Siberian Railway to Moscow. Here he met up with a friend, and the pair went on to Leningrad, the Ukraine, and on trains through the then Eastern bloc countries before inter-railing it home. He went up to Oxford (Brasenose College), and eventually emerged with a First in Politics, Philosophy and Economics.
"I always thought the thing about university was you could get most of your work done in three or four days, and the rest of the week you could enjoy yourself - but it was two essays a week, and quite hard work." He says he barely went to the Union or to the University Conservative Association, where aspiring Tory politicos - such as William Hague - usually cut their teeth. "I was interested in politics - but just not very interested in university politics," he says. "I chose to spend my time making friends, playing a bit of tennis (he was captain of the Brasenose tennis team), having fun."
Part of this was his membership of the Bullingdon Club, usually prefixed by the adjective "notorious", and famed for its habit of trashing restaurants, and other drunken antics. "Everyone asks me about this - and I'm not going to tell you anything about it," Cameron exclaims, with just a hint of exasperation. "We all do things that we probably shouldn't have done. I think that's probably one of them."
Leaving Oxford in 1988, he didn't really know what he wanted to do. He went for a few "milk round" interviews at banks, and management consultants. "I got offered one or two things, but nothing great." Then he saw an advertisement for the Conservative Research Department, and fell into his future career almost by accident. "It was in one of those careers bulletins that go round, which no one ever reads, but I applied for the job, and it just sort of clicked."
Cameron progressed quickly. Beginning in the Trade, Industry and Energy section, he was moved to the Political Section, became its head in 1990, and was soon briefing ministers for media appearances. When John Major became Prime Minister, Cameron was delegated to brief him for Prime Minister's Questions - working with David Davis. In the run-up to the 1992 General Election, he was running a team briefing Major for the daily press conferences, and then moved to the Treasury, working mainly as special adviser to the then chancellor Norman Lamont. Up ahead were the gathering clouds of Black Wednesday, and Britain's humiliating exit from the ERM. "It was an extremely difficult time for economic policy," admits Cameron, with some understatement. "There was not much peace at all."
Lord Lamont recalls first coming across Cameron at Central Office during the 1992 election. "I was very impressed by him; I thought he was very quick, very alert, and I thought I'd like to have him working for me," he recalls. "As soon as we'd won, I got in touch. He was a political rather than an economic adviser, so he would help with speeches; he would be in on briefings for parliamentary questions; he would be present at some of the tax meetings to do with the budget, and might give it a political angle. I felt that he would do extremely well - I was confident of that - and I also think he's very likeable. And I thought he would get into the House soon; though I hadn't envisaged he would possibly be leader of the party in such a short period of time."
He believes that if Cameron wins the leadership, the party should, as advertised, expect extensive reinvention - and points out his lack of experience in some areas. "I think he will give it a completely different image, because he's completely different from recent leaders; I think the idea of change will be embodied in him. But I think he would be ill-advised not to have a very balanced team, because he's got to keep the show on the road - and he probably doesn't know a lot about running the party in the House of Commons, because he hasn't been there very long. Although he's seen what it's like to be a minister, actually controlling the party - and three line whips and two line whips and discipline in the party - all that is a completely different game to him. He has seen none of that."
However he assesses Cameron as "very shrewd - and good at gauging reactions". Lamont believes he would make a good leader.
"He's generated a lot of interest; he obviously has a fresh and new appeal; and he has a lot of charm. He can be criticised as being a bit policy-light, but I think he's made a strategic decision to remain that way. I feel the only danger is that everything has come rather effortlessly; I don't think it'll be like that in the future. But having worked for me at a very difficult time, I'm sure he realises how very rough politics can be."
Is he likely to face resistance to reform from the Conservative old guard? "No," Lamont replies. "I think the mere fact that he looks like having a fairly decisive victory will buttress his authority. And I think people do want to win." Could that be a possibility at the next general election? "I never make predictions about anything , but I think it is conceivable that the double six might come up. He might win the leadership pretty comfortably, and I think against Brown he might look quite attractive to many people. My expectation is that he might have a slightly difficult time initially against Blair, and I think Brown might have quite a difficult time against him. Brown will not like being rivalled by a much younger person."
After the debacle of Black Wednesday (when Cameron can be glimpsed on news footage darting along the pavement behind a clearly exhausted Norman Lamont as the latter prepared to make the announcement that Britain was withdrawing from the ERM), he became special adviser to Michael Howard at the Home Office - then left the back-rooms of Westminster and Whitehall for seven years. He knew he wanted to become an MP - but knew that experience outside politics was vital. "It was quite a conscious decision," he says. He had met Michael Green, boss of media conglomerate Carlton Communications, which had just won the London ITV licence, and called him up.
"They offered me a job on the basis that I wouldn't fight the next general election - and I turned that down," Cameron recalls. But he later came to an agreement with them and worked there from 1994 until 2001, mainly as head of corporate affairs. ("Michael always used to say you can have any job title you want in order to get access to the meeting you need to go to - which I rather liked.")
Critics who insist that Cameron is all style and spin and no substance have claimed that, in Alastair Campbell's mischievous words, "you can't get much more spin-doctory than being PR man to a TV company". But Michael Green - who is a contributor to Cameron's campaign - says this was no languid schmoozing job.
"At the time we employed 14,000 people, and were capitalised at £6bn. He was absolutely involved in the plc, mergers and acquisitions, presentation, strategy, licences, investor relations in America, Europe and the UK," says Green, conjuring up a whirlwind atmosphere of buccaneering entrepreneurship. "We travelled all over the world together, and he would do the presentations sometimes - sometimes we'd get absolutely exhausted, the finance director and me, and we'd say: David, for Christ's sake, can you do this one? - and he did. And he did it better than us sometimes. He was definitely board material. We had some very big heart-to-hearts, and I tried to persuade him that he could have a really good career in the industry. But he was completely resolute about going back to politics, and I respected him for that. He's good - he's the real McCoy."
Cameron went part-time at Carlton to fight his first seat - Stafford - in the 1997 general election. "It was a marginal we were meant to win if we were going to win the election, but obviously in the '97 landslide you just got washed away with the tide," he says. "I worked at it very hard, I really did. My memories of that night are listening to the exit polls on the way to the count, and hearing the Sunderland South result, which was like a 10 per cent swing to Labour. And I just thought: 'Right - I'm toast.'"
He says he took this setback as philosophically as he could. "I remember being back at our cottage in the constituency, lying on the sofa the next day, thinking: Well, it's not the end of the world. Michael Green rang and said: Come back to your job - and that was fine. But it's obviously disappointing and you felt you'd let down people who desperately wanted you to win."
After another four years at Carlton, Cameron finally came home, winning the safe seat of Witney in 2001, close to the Home Counties turf where he grew up. "This is very familiar territory, and I just feel very much at home with the people here; it's that mixture of countryside and market town and also quite close to London so a lot of people have business there or go there to work - it's a mixture that I totally get." And on a sunny constituency day last week, out in the gentle Oxfordshire countryside, he looks completely at ease, despite another packed schedule which starts with an 8am address to the Business Breakfast Club at the Blue Boar in Chipping Norton, and ends that night with the switch-on of the Christmas lights in Witney. ("It sounds wonderful," he says "I'm going to be in an open topped bus with the Harry Potter lookalike competition entrants. I don't think I'm one of them."). And after that, his diary compiler appeals, he will "try and pop over to the Rotary Club charity pig roast at the Town Hall". In between, there's a lecture to politics students at a local college, a visit to a schools politics competition, a meeting with local councillors, another with Make Poverty History campaigners, and his surgery. And he's already taken a call from Samantha, in which he's promised to do the shopping, and cook the supper. "Don't worry. It'll all be ready and lovely when you get here," he assures her.
She and their children are arriving tonight from their London house - usually described as "in Notting Hill", although it isn't quite. ("There are certain arguments in life you just have to give up on - and that's one of them," he admits, laughing. "We're selling at the moment, so I should probably claim it's in Chelsea.") The couple first met as teenagers (Samantha was a friend of his younger sister Clare.)
Her background is, if anything, even more patrician than his own. Now design director of venerable Bond Street stationers and accessories firm Smythsons, she was brought up on the 300-acre Normanby Hall estate, near Scunthorpe, the daughter of Sir Reginald Sheffield. Her mother, Annabel Jones, owned a Beauchamp Place jewellers and now runs a furniture business, Oka. Her stepfather is Viscount Astor, a minister in the Major government and a director of Urbium, the Tiger Tiger bars and clubs group, of which Cameron was also until recently a director - which embroiled him in controversy in the binge-drinking debate and earned him a toe-curling inquisition by Jeremy Paxman. (He has now resigned from the group following a take-over.)
A former Bristol art student, Samantha has been credited with helping turn Cameron from an allegedly stuffy "Tory boy" into a more relaxed and open character. They celebrate their 10th wedding anniversary next year. "She's been a big influence, because she's not that interested in politics, so she's a really good reality check on life," he says. "She's got her own life and career, and someone who's not interested in politics can sort of see the big picture - it's very helpful because they don't get caught up in the minutiae."
Between the business breakfast and the politics lecture, he dashes home to switch on the heating at their tastefully converted barn in a tiny village near Chipping Norton. He says he loves it here: taking the children swimming on Saturday mornings, or to the farm down the road where he sits in the kitchen chatting over tea while Nancy, 22 months, plays with the puppies; and growing vegetables. His courgettes, tomatoes, "and something else - I think it was apples" took first prizes at the summer flower show. "Samantha says that no one between the ages of six and 60 takes part in these contests, so it's deeply sad," he smiles.
He talks lovingly of their son Ivan, nearly four. "He is very, very disabled," says Cameron. "It's a huge thing to happen, because of the difference between the child you were expecting and what you have. He's wonderful, and lovely, and we adore him. But it was a big shock, and takes a long time to get over. And it is tough. But we're very lucky because we can afford extra care and we can manage - and I think we're better parents for recognising that we're not perfect, so we're better for doing what we can, rather than pretending we can do everything which would probably cause us completely to collapse."
Cameron has campaigned vigorously on behalf of disabled children and special schools, and is proud of an e-Politix award he won for his work on this. "The school he goes to is very important because they are so brilliant at just very intense therapy. And there's a little book we fill in every day about how his night was, and they fill in what he did during the day - and it makes wonderful reading." He says he and Samantha have relied only on the NHS for Ivan's care, and have spent a "vast amount of time" in hospitals. "Sometimes I was sleeping on the floor and going into the House of Commons the next day. We took it in turns."
Appointed shadow education secretary in May, Cameron has also served as Shadow deputy leader of the house, deputy chairman of the party, and on the Home Affairs Select Committee. As Michael Howard's policy coordinator, he played a key role in the last election campaign - useful battlefield experience if he is chosen to lead the party. Could he successfully transform it, and achieve a different result next time?
If victory depended solely on the "heart-melting test" and the "chat in the pub" test, then he possibly could. Genuinely charming, with a nice line in self-deprecating remarks, he wears his Eton and Oxford background so lightly that, unless you knew, you would hardly guess it was there. But it's still very different from that of the majority of voters he's seeking to impress - more Macmillan than Major. And with his vision of a "modern, compassionate Conservatism", he will be leading core Tory voters out into unfamiliar centre-ground terrain, with, at the moment, only sketchmaps. Will they be brave enough to follow him? And how many non-Tory voters will be tempted to buy his wares, marked "Made in Notting Hill" on one side, and "Compassionate" on the other?
Nearly 800 people turned up to hear Cameron and Davis at the Cambridge hustings last week. As the faithful trooped in, mostly middle-aged or elderly, it was hard not to see them as a somewhat lost tribe, cast adrift uncomprehendingly in the brash modern Britain of Pop Idol and binge-drinking. With the triumphalism of the Thatcher era no more than a hazy memory, the mood is cautious, even subdued - despite the best efforts of the upbeat young party workers, with their stalls of David Davis badges, and David Cameron mints ("a breath of fresh air"). Cameron had told me earlier that day that he had never lost faith in the party, not even in the darkest days since its colossal 1997 defeat.
"There was a time after '97 when even if you'd had Einstein, Wittgenstein and Mother Teresa rolled into one, we weren't going to have an early Conservative recovery," he had said. "There was just no prospect of it - I actually thought that William Hague's first moves in terms of trying to broaden the appeal of the party were right; but it was an impossible task.
"But I never lost faith because I always thought that at the end of the day, if you are a politician who believes in individual freedom and open markets and national sovereignty, and if you are a politician of the centre right, and if you stick to your views and explain them and make sure that you're in touch with your country and people's aspirations, the centre right position is popular, and right, and sensible, and it will come back again."
If he's lucky, and the polls are right, work starts Tuesday. Just at the moment, though, "Pop Idol Britain" may take some convincing.
David's friends, a who's who
George Osborne, 34: CAMPAIGN MANAGER
Shadow Chancellor and MP for Tatton since 2001, key friend and lieutenant of Cameron.
Catherine Fall, 35: CHIEF OF STAFF
Old friend of Cameron and was among the first to join the campaign. Worked on foreign affairs and business liaison for Michael Howard.
George Eustace, 34: HEAD OF PRESS
Deputy Press Secretary to Michael Howard in the 18 months leading up to the election.
Gabrielle Bertin, 27: PRESS OFFICER
Press Officer to Liam Fox when he was co-chairman of the Party. Worked for Cameron in his role as shadow education secretary.
Sophie Pim, 31, and Liz Sugg, 28: EVENTS ORGANISERS
Both played key role in Michael Howard's tours and appearances at the May General Election.
Steve Hilton, 36: STRATEGIST/CAMPAIGNS
Formerly in advertising, worked for Maurice Saatchi. Old friend of Cameron. Has played leading role in focusing campaign message.
Dan Ritterband, 30: FIXER
Former "trouble-shooter" in Michael Howard's office. Ex-ad account handler at Saatchi and Saatchi.
Fiona Melville, 29: CONSTITUENCY CAMPAIGNS
Ex-Conservative Research Department, and head of the Tories' Lib Dem "attack unit" during the last General Election.
Oliver Letwin: SHADOW ENVIRONMENT SECRETARY
Free market enthusiast and early supporter who is likely to have a key role in overhaul of Tory policy.
MPS WHO HAVE PLAYED KEY ROLES
Andrew Robathan, Michael Gove, Ed Vaizey - all close friends of Cameron who have helped formulate policy and campaign strategy from outset.
The Cameron position on...
"The flow of new regulation from the EU must be reduced: our aim should be to take back control of employment and social regulation." Opposes joining the euro.
Reduce and simplify taxes. "This means proper control of public spending, and a long-term strategy for tax reduction."
"We will never get good schools, universities, hospitals, transport or police on the cheap - we must share the proceeds of economic growth between tax reduction and public service investment."
More parental choice; reforms to give schools autonomy. Restore the credibility of A-levels; radical reform of the Qualifications and Curriculum Authority (QCA). "I am ready for a huge battle with the educational establishment to banish the 'progressive' theories that have done such damage for so long."
More autonomy for hospitals; fewer barriers between NHS and private providers; no "patient passports".
"Uncompromising approach" to extremist terrorism; review of lessons to be learnt from the attacks on the London Underground and of resources for intelligence services. "The measures we take must never undermine the very liberal values we're seeking to preserve. So: no ID cards, no religious hatred laws."
"We should now establish a cross-party commission to create a long-term framework for energy and the environment." A statutory framework for reducing carbon emissions, and a Carbon Audit Office.
"The principle [we] should support is controlled and fair immigration. That is the flip side of good race and community relations."
Policing and crime
Substantially increase police numbers; elected police commissioners; emphasis on neighbourhood policing of low-level crime. "Stiff" minimum sentences for serious crime.
Voted in favour of military action. No withdrawal now: "We have a responsibility to see the job through."