If you want to see a physical demonstration of how the Westminster system marginalises the Liberal Democratic Party, pay a visit to Nick Clegg's office. It is pitifully small, in what feels like one of the Palace of Westminster's lost attics.
Outside Westminster, the media treat the leader of Britain's third party with similar condescension. My meeting with Mr Clegg occurs the day after he had made his first significant speech on foreign policy, at Chatham House, marking his first half-year as leader of the Liberal Democrats.
It was a thoughtful and lengthy speech, including a refreshingly specific analysis of the conditions under which British support for a military invasion of Mugabe's Zimbabwe would be justified. Yet there is no coverage in the media at all: not a single word in a single newspaper. To make matters worse, all over the front page of The Times are Paddy Ashdown's somewhat garbled observations about Zimbabwe. I tell Clegg that he might as well have turned up at Chatham House, decided not to make a speech, and just had a jolly good lunch instead.
"If you're inviting me to vent my spleen about why it is that Liberal Democrat leaders traditionally don't get as much coverage as they think they should, we would probably be here all day. And all night. And for the rest of the week. It is a little galling sometimes to do all that hard work and then ...."
I suggest that one reason may relate to Nick Clegg, rather than to the Lib Dems as a whole. Vince Cable, while acting leader after Sir Menzies Campbell's resignation, constantly grabbed the headlines with his dazzling performances in the House of Commons against Gordon Brown. Isn't the truth that the Lib Dems have only one star, and it isn't the current leader? Clegg flushed, as he did several times during the interview: one senses a temper beneath the smooth exterior.
"I don't think Vince would accept that for a minute. You should ask him yourself. I'm not the slightest bit interested in describing the Liberal Democrats or other leading politicians in terms of stars and celebrity ... but it's only a source of delight for me as party leader to have in Vince someone who's eminently more credible than George Osborne in the economic circumstances facing the country. Is this a problem? No, it's a massive, massive plus for the party. Thank heavens our party is no longer defined purely by one person." As Clegg is saying this, I wonder if he is referring to the period of Paddy Ashdown's leadership, Charles Kennedy's, or both. Anyway, the current leader of the Lib Dems continues his retort to my slightly insensitive question about the brief but dazzling period of Vincent Cable's leadership.
"I just don't think you can compare, and I don't think Vince would like to compare, what it's like to be interim leader with someone like myself who knows that my impact would be a cumulative one over a long time."
So you're pacing yourself? The handsome Clegg visage colours briefly once again.
"No, I'm not pacing myself. On issues like energy and fuel poverty, I'm the only person talking about it at PM's Questions. With Zimbabwe, I was talking about it long before Cameron and Brown even dared to, and on Burma, and on the plight of our armed forces ..."
To the extent that Clegg has managed to make an impression when up against Gordon Brown in the House of Commons, it has indeed been on the issue of the British Army in Afghanistan. He has made telling interventions about the inadequacies of our troops' equipment. So, I asked Clegg whether he ever feels that the Prime Minister and the Defence Secretary, Des Browne, are being hypocritical when they regularly intone their sorrow at the death of yet another British soldier.
"I'm reluctant to point a personal finger of hypocrisy, at Des Browne in particular, because he has been out to see the forces on several occasions, to parts of Afghanistan where no other politician has been allowed to venture. I think Gordon Brown himself has clearly displayed a crushing indifference towards the military. It's an open secret at Westminster. But to say that Gordon Brown is indifferent to the plight of individual soldiers when an increasing number of them are being killed in Afghanistan is not an allegation I'd want to direct at him."
In the half year since Clegg became Lib Dem leader, Gordon Brown has gone from hero to zero. Yet, I asked him, why is it that, at least so far as the opinion polls indicate to us, the Conservatives have gained enormously as a result, but the Lib Dems scarcely at all?
"You are inviting me to say that the glass is half-empty when I think it's half full. I'm not innumerate. I can read that the polls are swinging in favour of the Conservatives. Do I think they are sustainable or permanent? No, I don't. I think a lot of people who are commentating on politics completely overlook the frothiness and the febrile nature of the opinion polls. The average Conservative poll lead over Labour, the day before the March Budget, was only about 2.7 per cent. It's all happened very recently. Last summer they were writing the political obituaries of David Cameron."
It's interesting that at several junctures Nick Clegg brings Cameron's name into the discussion, even when my questions didn't specifically mention the Tory leader. When I ask Nick Clegg whether he thinks the surge in Conservative support is entirely down to the deficiencies of Gordon Brown or Labour, he graciously acknowledges the Cameron effect.
"David Cameron has been very disciplined at trying to remove the negatives about his party, and he's said why people should want to vote for him. He hasn't quite told us what he would do once he's closed the door of No 10 Downing Street behind him, but he's removed those negatives. I certainly know from travelling around the country that not only have people turned their back on Gordon Brown and Labour, they're not even listening any more.
"That's why I think it will be extremely difficult for them to recover under whatever alternative leader they choose. I think that both opposition parties, the Conservatives and Liberal Democrats, see much more clearly than Labour that the great sea-change in British politics is that the experiment in big government has failed, it hasn't delivered the more socially mobile, socially just society that it purported to and, in any event, can't be sustained financially in the way it has over the past few years."
So could Nick Clegg see himself serving in a Cabinet led by David Cameron?
"I'm not going to spend a millisecond reflecting on that because it's not going to happen; I'm not going to lead an annex to a Conservative or a Labour Government."
But if there was a hung Parliament, with the Tories as the biggest single party, then the offer might come from Cameron, mightn't it?
"I can't envisage the circumstances in which just because I'm invited I would sit in someone else's Cabinet. How would that achieve a more liberal Britain?"
"You'd have that influence on Government."
"What? Just by having a couple of bums on seats?
That seems a rather dismissive way of describing his colleagues. But, seriously, isn't the point of politics to play some part in Government? Even the Liberal Democrats have to lose their virginity one day, surely?
"The more you press me on this question, the more you should see how implausible your scenario is. There is going to be no great coalition government in this country other than following a change in the political system. Coalitions follow from political systems which produce them ... I'm not even going to hint that we would merrily sit around the table with either a Labour or a Conservative Prime Minister without seeking substantive reform in the direction we want to see Britain go."
I suggest to Nick Clegg that his insistence that he wouldn't join forces at Cabinet level in a hung parliament with either main party was not so high-minded. Isn't it more because to say that he might link at governmental level with Cameron would deter those "soft" Labour voters who might be thinking of switching to the Lib Dems, but would never vote Conservative – while to imply he might ally with Labour would deter voters in the South of England?
"You may scoff, Dominic, but there is a high-minded aspect to this, if I may say so. In any case, do I think it is mathematically likely or even possible that Labour and Conservative will have a complete photo finish with exactly the same number of seats, so that – voila! – Nick Clegg can play eeny meeny miny mo? It won't happen like that. If there is no party with an overall majority, then the party with the most seats will have a moral mandate, clearly not strong enough to govern on their own, but to put forward their ideas on how they intend to govern and then to seek ad hoc or even more permanent arrangements with other parties .... What I do accept completely is that as someone who is seeking to gain more seats and more votes and so gain greater influence on the way Britain is run, it is my job to be ever more explicit about what the Lib Dems' priorities are – and some of them are already fairly obvious."
Is it so obvious? Nick Clegg mentioned a commitment to cutting taxes several times in our discussion; but there is nothing as clear and totemic as Paddy Ashdown's slogan of an extra penny on the basic rate, to fund education, or Charles Kennedy's distinctive position – distinct from the two main parties, that is – against the war in Iraq. Why, I asked, hasn't the current leader of the Lib Dems in his turn managed to come up with a single clear message or big idea that tells the public in the most simple way what he and his party stand for? This elicits another Clegg flush.
"If I had that big idea – and I've given you some indication of where I think it might lie – do you think it would be sensible for me to unveil that concrete policy two years before the general election? Have Labour and the Conservatives done that? Do you know what single issue the Conservatives stand for? No. Do you know what single issue Labour stands for? No. But we are clearly headed, more than any other party in British politics, towards an aggressive tax-cutting approach for the vast majority of ordinary income families in this country."
I say that I somehow doubt that there are enough super-rich who will stay rooted to the spot long enough to pay the extra taxes necessary to fund "aggressive tax-cuts for the vast majority of ordinary income families" – but the Lib Dem leader insists that his plans "have been worked out".
Our conversation took place before the result of the Henley by-election, in which the Conservatives gained more from the collapse in the Labour vote than did the Lib Dems. Clegg insists that he has spent time in his own part of the country "knocking on people's doors to try to find out what they thought about the Cameron effect".
"Time and time again people would tell me: 'it's all very well, but the Conservatives now would say anything that people would want to hear'."
I point out that this shows that the Conservatives really have stolen the Lib Dems' old clothes. Mr Clegg's charming press secretary, who is sitting with us, stifles a giggle. Her leader's face flushes for the last time and tells me that I have "made a facetious remark".
Despite this, Nick Clegg does actually have a sense of humour. Without that, after all, it would be difficult – if not unbearable-– to be leader of the Liberal Democrats.