MI6 is playing down its claim seized on by the government before the invasion of Iraq that Saddam Hussein's forces could deploy chemical and biological weapons within 45 minutes, intelligence sources have told the Guardian.
MI6 is distancing itself from the notorious claim as Lord Butler is expected to criticise the agency, along with Whitehall's joint intelligence committee, and Downing Street, in his long-awaited report to be published on Wednesday.
Lord Butler and his team of privy counsellors are known to be concerned about how flawed intelligence and politically inspired analysis rather than facts were used to back up the case for military action.
Downing Street as well as the country's spymasters was showing signs of growing nervousness as two former senior defence intelligence officers last night joined the fray, questioning assertions made by Tony Blair about Iraq's weapons programme to MPs and at the Hutton inquiry.
Sir Richard Dearlove, the head of MI6, appeared to attach great importance to the 45-minute claim, which appeared, without any qualification, four times in the government's Iraqi weapons dossier published in September 2002.
He told the Hutton inquiry that it came from "an established and reliable source a senior Iraqi military officer". Yet intelligence officials now admit there was little new in the claim and that it was "not surprising". They say the 45-minute claim could have been deduced from what was known about Iraqi military capabilities in the 1980s during the Iran-Iraq war.
In a little-noticed passage, the parliamentary intelligence and security committee noted in a report published after the invasion of Iraq that the claim "added nothing fundamentally new to the UK's assessment of the Iraqi battlefield capability".
However, the 45-minute claim gained added significance before the war as it was used to bolster the assertion that Iraq "has continued to produce chemical and biological agents".
That assertion, of which there is no evidence, was described in the dossier as "recent intelligence". This was wrong, intelligence officials now say. But it was backed up at the time by John Scarlett, head of Whitehall's joint intelligence committee, and subsequently repeated by Mr Blair.
The 45-minute claim is believed to be among the intelligence referred to in last night's BBC Panorama programme as having been "withdrawn" by MI6.
Brian Jones, a former defence intelligence official, told the programme, A Failure of Intelligence, he was "confused" and "couldn't relate to" Mr Blair's evidence to Hutton, notably the reference to a "tremendous amount" of information about Iraq's WMD programme.
"Certainly no one on my staff had any visibility of large quantities of intelligence," said Dr Jones, whose questioning, and that of his colleagues, about the accuracy of the dossier as it was being drawn up was ignored by more senior officials.
John Morrison, former deputy head of the defence intelligence staff, told the programme that when Mr Blair told MPs the threat from Iraq was "current and serious" he could "almost hear the collective raspberry going up around Whitehall".
He added that Downing Street's last-minute call for more intelligence to put in the dossier reeked of "scraping the barrel".
Mr Morrison also referred to operation Desert Fox, the three-day bombing campaign against Iraq in December 1998. Defence intelligence officers felt pressured after the operation to sign up to the claim that targets actively involved in WMD production had been hit in the strikes when they were not certain that was the case, he said.