The damaging e-mail by Jonathan Powell, disclosing his concerns about the draft dossier on Iraq's weapons, suggests the doubts over the Government's central claims about Saddam Hussein's arsenal went to the very heart of Tony's Blair inner circle.
Mr Powell's message, arguably the most explosive piece of evidence revealed to Lord Hutton's inquiry so far, hints at the air of disappointment inside Downing Street. It was sent to John Scarlett, who as chairman of the Joint Intelligence Committee (JIC) was in charge of drawing up the document, on 17 September last year, a week before the final version was unveiled by Mr Blair.
At the time, there was growing speculation that the Prime Minister was about to join President George Bush in an attack on Iraq. Mr Blair, who had recently met the US President at Camp David, was anxious to stress that military action was not imminent, while steadily building the case for the Iraq issue to be addressed.
Mr Powell hinted that the dossier as drafted might not win over hostile MPs. His e-mail could be read as an admission that the man at the hub of Mr Blair's circle believed the case against Saddam was pretty wobbly all along. Mr Powell conceded that "the document does nothing to demonstrate a threat, let alone an imminent threat from Saddam". That is an uncanny echo of the resignation statement by Robin Cook on the eve of the war.
The Powell e-mail is also bound to fuel suspicion that the dossier may have been "sexed up" after it was sent. If true, that would prove further corroboration for the main thrust of the claim by the BBC's Andrew Gilligan which ignited the war of words with Downing Street. Another version of the dossier was produced two days later, although the details of that draft have not been disclosed by the Hutton inquiry. The final version was given to MPs on 24 September, allowing more time for it to be "hardened", as Martin Howard, deputy chief of defence intelligence, conceded last week.
So it would be no surprise if the language was toughened up in the wake of Mr Powell's memo. In another e-mail disclosed yesterday, dated 5 September, Alastair Campbell told Mr Powell there would need to be a "substantial rewrite" of the dossier. Significantly, this was to reflect Mr Blair's wishes, or, as Mr Campbell put it: "Structure as per TB's discussion." There is also a hint that Mr Blair was pressing the intelligence services to allow more of their material to be used in the document.
We also know from documents posted on the Hutton inquiry website that the title of the document was "sexed up" in the final days before publication. The 19 September version was entitled Iraq's programme for weapons of mass destruction. Yet the final version was called simply Iraq's weapons of mass destruction. This change is rich in irony because Mr Blair has subtly but significantly toned down his claims that WMD would be found in Iraq to say that "evidence" of weapons "programmes" would be uncovered. So the wheel has come full circle.
The other important thing about the Powell e-mail was that Mr Blair appeared to ignore his chief of staff's advice when he unveiled the dossier a week later. Mr Powell, a former diplomat, urged a cautious approach, saying: "We will need to make it clear in launching the document that we do not claim that we have evidence that he [Saddam] is an imminent threat."
Yet on 24 September, the Prime Minister did no such thing. In his foreword to the dossier, Mr Blair wrote: "I wanted to share with the British public the reasons why I believe this to be a current and serious threat to the UK national interest." He had become "increasingly alarmed" by evidence from inside Iraq that Saddam was continuing to develop WMD. "The picture presented to me by the JIC in recent months has become more not less worrying," he added. "I am in no doubt that the threat is current and serious, that he has made progress on WMD, and that he has to be stopped."
The recently acquired intelligence that Iraq could deploy chemical and biological weapons within 45 minutes --which first appeared in a draft on 10 or 11 September - was added to the mix by Mr Blair, capturing newspaper headlines and suggesting that the Iraqi threat was imminent.
Ministers insist they never used the word "imminent". Yet their campaign was designed to be as dramatic as possible in an attempt to answer the "why now?" question posed by Mr Cook and many Labour MPs. It is a question that many critics of the war believe was never answered.