Of the hundreds of documents supplied to the Hutton inquiry, three stand out. One is the extract from Alastair Campbell's diary, by virtue of an aggressive profanity that speaks volumes of the passions raging around the Prime Minister. The other two are e-mails from Jonathan Powell, the Prime Minister's Chief of Staff, which catch the eye for a very different reason. They stand out for the clarity of their argument and the substantive nature of their communication.
The first, dated 17 September 2002, warned Tony Blair about the publication a week later of the famous dossier on Saddam Hussein's weapons of mass destruction: "We need to make it clear in launching the document we do not claim we have evidence it is an imminent threat. The case we are making is that he has continued to deploy weapons of mass destruction since 1998 and is in breach of UN resolutions. Unless we check him at that stage, he will become a serious threat to all of us."
Despite the fact that, as Powell told the Hutton inquiry last month, this was a point "which I repeated in subsequent e-mails", the Prime Minister sailed close to the wind in the House of Commons, describing the threat from Iraq as "serious and current" and allowing an impression of imminence and urgency to hang over the debate.
The other e-mail, revealed this week, was the final big surprise sprung by the inquiry, after seven weeks of unexpected turns. It was sent to John Scarlett, the intelligence chief drawing up the dossier, on 19 September 2002, just after the deadline for final comments.
Referring to a column by The Independent's chief political commentator, Powell said that one paragraph "backs up the Don McIntyre [sic] argument that there is no chemical and biological weapons (CBW) threat and we will only create one if we attack him. I think you should redraft the para".
Scarlett went one better, and dropped it altogether. On the face of it, a "clear win" for those who accused Downing Street of hardening up the dossier at the last minute.
But Powell went on to say: "My memory of the intelligence is that he has set up plans to use CBW on Western forces and that these weapons are integrated into his military planning."
What he was saying, therefore, was that he understood the raw intelligence that Scarlett was collating better than Scarlett did himself. Scarlett implicitly accepted this by making the change.
Powell's e-mails appear to point in different directions. One warned against over-egging the threat from Saddam; the other egged it, but "within the bounds of the available intelligence", which was the brief given to Scarlett. Yet the contrast reveals Powell's usefulness to the Prime Minister. It shows his fastidiousness, his care to ensure that the Government's presentation was soundly based on the evidence - however dud that later turned out to be.
With the departure of Alastair Campbell, who has been Blair's press secretary for as long as Powell has been his Chief of Staff, Powell's role at the heart of the Blair Government becomes even more important. He has been at Blair's side since 1995, the year after Blair became leader, and so has accumulated authority simply by length of self-effacing loyal service. Of the original pre-election clique, Peter Mandelson, Anji Hunter and now Campbell have all gone. Although Mandelson, the twice-resigned Cabinet minister, has been back in Downing Street since Campbell's resignation, it is unlikely that he will erode Powell's mastery of the No 10 machine.
Powell therefore has already fulfilled much of his life's ambition, which is to match the achievements of his more famous eldest brother, Charles. Charles, his senior by 15 years, became one of Margaret Thatcher's most favoured advisers. He was with her when she did business with Gorbachev, but his formal position was never higher than that of foreign affairs secretary at No 10. Jonathan has a grander title, explicitly responsible as a political adviser with executive powers over civil servants for the Prime Minister's office.
He was intimately involved in events almost as momentous as the fall of the Berlin Wall. He was with Blair while the Good Friday Agreement was negotiated in Northern Ireland. Then he acted with sinuous flexibility as the Unionist counterweight to Mo Mowlam's nationalist sympathies and, without missing a beat, as the nationalist balance to Peter Mandelson's tilt to the unionists. With Blair now on his fourth Northern Ireland Secretary, Paul Murphy, Powell remains the Prime Minister's constant personal emissary, still often deputed to fly to Belfast on the boss's behalf.
He was a member of the war cabinet that was convened for Iraq in 1998, reconvened for Kosovo, then for Afghanistan and, this year, Iraq again. And he has been just as committed as Blair in pushing the rock of Israeli-Palestinian peace talks up the hill every time it rolls back.
Thus he has greater influence than his brother had, yet Charles is a grander, more establishment figure than he will ever be. They are very different. Charles is a networker and an anecdotalist, whereas Jonathan, although he can be imperious, is both plainer and more technocratic. It is difficult to imagine Charles padding around conference hotel corridors in his socks, as Jonathan has done, overseeing the prime ministerial speech-writing. The fraternal competition for access to power continues, however. Charles's wife Carla, the extravagant society hostess, reportedly entertained the Prime Minister's wife and daughter on a short additional holiday at her place in Italy this summer.
There was something about the Powell family dynamic that drove all four brothers to overachieve. Their father, Air Vice-Marshal John Powell, was the son of a Welsh hill farmer who once campaigned for Keir Hardie, the first leader of the Labour Party. John went to Cambridge University on a choral scholarship where he met Geraldine Fitzgerald Moylan, a classical scholar from an aristocratic family. Their four sons went to private schools - Jonathan rebelling against the traditional regime at King's, Canterbury, much as Blair kicked against the trammels of his public school.
Charles, with typical condescension, once expressed surprise at his youngest brother's claim to be a "lifelong supporter" of the Labour Party. But Jonathan was always on the left, declaring himself a Maoist at the age of 14. After a series of short-term jobs, he followed Charles into the Foreign Office, suppressing his political affiliation in civil-service neutrality. Middle brothers Chris and Rod, meanwhile, went into advertising and computers respectively, in which they both made fortunes. Chris, like Jonathan, is a Labour supporter, who worked on the 1997 election campaign, while Rod is a senior vice president of Invensys in the US.
Powell's great break came in 1991 when he was 35, and became political secretary at the British Embassy in Washington. He had first worked there a decade and a half earlier, when he was second undergardener, a holiday job he got as a student when Charles was a diplomat at the embassy.
At about the same point in the US presidential election cycle as we are in now, Powell spotted Bill Clinton among the several dwarves then jostling for the Democratic nomination - against, oddly enough, a President Bush who had just won a war against Iraq but was just beginning to look electorally vulnerable.
When Gordon Brown, the shadow Chancellor, and Tony Blair, shadow Home Secretary, came to Washington 15 months later to learn "how Clinton won it", it was Powell who managed the trip. Thus was the least-noticed of the central relationships of the Blair Government born.
He made an immediate impression on the Blair team when he joined it after the 1994 leadership election. They found his civil service ways both reassuring - here was someone who knew something about government from the inside - and faintly comical - he had the unfamiliar habit of taking minutes. (He became less punctilious, however: he told the Hutton inquiry there was no record of some of the meetings it was interested in because "there is no purpose served by minutes" - unless there are "action points that need to be taken forward".)
He was a smart choice for Blair. Not only is he highly effective - "when he says he'll do something, it gets done," says an admirer - but he is driven, focused and discreet. As an added bonus, his brother was able to act as a vital channel of communication with Baroness Thatcher, who anointed Blair with her implicit blessing before the 1997 election.
Like Campbell and Blair himself, he is typical of New Labour Man. He has two grown-up boys from his marriage to Karen, an American. One starts at Essex University this term; the other has just graduated from McGill University in Canada.
For all his time in government, he has lived - unmarried like Campbell and his partner Fiona Millar - with Sarah Helm, former Europe editor of The Independent. They have two primary-school-age daughters and Powell manages to spend time with them in a way that would have been unthinkable of previous generations.
Powell has survived by quiet efficiency and by avoiding the mistakes of Campbell and Mandelson of putting their pride above loyalty to the boss. Despite the historical importance of his evidence to the Hutton inquiry, his ability to melt into the background will ensure he escapes criticism, but the gradual erosion of the old New Labour core around Blair raises the question of when he might move on to earn some serious money and spend more time with his young children.
He used to say to friends that he would like to stay in Downing Street until he had seen the euro referendum through. Now that this seems a remote possibility, the question of the timing of his eventual departure becomes more awkward. If he does go before Blair does - unlike Charles, who stayed with Thatcher to the end - the Prime Minister might find himself more seriously weakened than he was by the departures of Mandelson, Hunter and Campbell before him.
Born Jonathan Nicholas Powell, 14 August 1956, fourth son of Air Vice-Marshal John Powell and Geraldine (née Fitzgerald Moylan)
Family Married Karen Drayne, 1979 (marriage dissolved 1997), two sons, 21 and 18; partner Sarah Helm, two daughters, five and four
Education King's School, Canterbury; University College, Oxford (History 2:1); University of Pennsylvania (second degree in history)
Career Quick-order chef, Little Chef, Hampshire; second undergardener, British Embassy, Washington DC; trainee journalist, BBC and Granada TV, 1978-79; Foreign Office 1979-95, including postings to Lisbon, Stockholm, Vienna and Washington; Chief of Staff to Tony Blair, as Leader of the Opposition, 1995-97, and as Prime Minister, since 1997
Recreations "Hyphenated sports" (Who's Who)
He says "We are likely to see a transition from a feudal to a Napoleonic state" (of the new Blair Government)
"Alastair - what will be the headline in the Standard on day of publication? What do we want it to be?"
They say "We are all basically strivers. Maybe that's what I had in common with Margaret Thatcher and perhaps that is what Jonathan has in common with Tony Blair." Charles Powell, eldest brother