BBC One's Panorama investigates the events leading up to the Iraq war to see if there is any truth in claims that Tony Blair misled the country.
On 23 July 2002 the prime minister chaired a highly sensitive meeting.
It may prove to have been one of the most significant on his road to war in Iraq.
The BBC's Panorama programme has been told by several reliable sources that MI6 chief Sir Richard Dearlove was minuted as saying that "the facts and the intelligence" were being "fixed round the policy" by the Bush administration.
By fixed, it is understood that the head of MI6 meant the Americans were trawling for evidence to support a policy of regime change.
Just back from Washington, Sir Richard reported that military action was inevitable. In the same meeting, and not for the first time, Foreign Secretary Jack Straw questioned whether Saddam Hussein posed a sufficient threat to justify invasion.
Panorama has also learnt that the government tasked MI6 to extract as much information as possible from their limited sources in Iraq to build up an intelligence case.
The results of this new intelligence trawl were intended to support a new dossier which was subsequently published on the 24 September 2002.
Dr Brian Jones, the chief Weapons of Mass Destruction (WMD) analyst at the Ministry of Defence (MoD), recalls that there was "an appeal... [for] people to look and think very closely about the evidence that was available."
News of the government's dossier on Iraq's WMD threat, first reached Dr Jones in the summer of 2002.
"It was mentioned to me by a colleague in the margins of a meeting in Whitehall. Our shared reaction was that that would be a considerable challenge because of the relatively sparse nature of the intelligence available on Iraq's WMD."
'Lack of candour'
Robin Cook, the former foreign secretary who resigned over the Iraq war, says of the prime minister's actions that "... he knew perfectly well what he was doing... I think there was a lack of candour.
"I think the real dishonesty of the government's position is that Tony Blair could not be frank with the British people about the real reason why he believed Britain had to be part of an invasion which was to prove to the US president that we were his most reliable, most sound ally.
"His problem was he could not be honest about that with either the British people or Labour MPs, hence the stress on disarmament."
His view comes alongside further evidence from senior figures which once again bring into question the validity of pre-war claims made about Iraq's WMD programmes.
Adolfo Aguilar Zinser, the former Mexican ambassador to the UN, was invited to a private intelligence briefing about the WMD evidence.
"I asked them, 'Do you have full proof of the existence of these weapons, at any one of these particular sites that you are referring to?' And the MI6 officer told me: 'No, we don't'."
He continues by saying: "... it was very clear they didn't have the proof, that they had circumstantial evidence of a funny behaviour, of a suspicious behaviour.
"But I knew that, we all knew that, because that was what we were getting from the inspectors."
The former secretary of the Defence Notice Committee, Rear Admiral Nick Wilkinson, told Panorama: "... the government perhaps allowed the public to be misled as to the degree of certainty about weapons of mass destruction."
Sir Stephen Wall, the prime minister's former European affairs advisor says on the matter that "We stretched the legal argument to breaking point in my view..."
Number 10 has told Panorama that the Prime Minister has nothing to add to the facts and findings of the four inquiries that have already been held.
Panorama: Iraq, Tony and the Truth on BBC One at 2215 GMT, Sunday 20 March 2005.