At his weekly question and answer session in the House of Commons, Blair insisted that "in relation to the allegations that have been made, there is not a shred of truth" in them.

Asked if he would give evidence to an investigation by the Foreign Affairs Select Committee, the prime minister told deputies: "In accordance with convention, I will not attend that committee," although Foreign Secretary Jack Straw would.

However, Blair said he would "cooperate in any way at all" with a separate inquiry by parliament's joint intelligence and security committee -- which meets behind closed doors, and whose reports are subject to censorship by Downing Street.

Blair has for weeks been forced to defend himself against charges made by the media and seized upon by the opposition that his office tried to make Saddam Hussein's regime appear more menacing by embellishing a dossier on weapons of mass destruction, published in September, before the US-led war against Iraq.

Unnamed sources told BBC radio that a line in the government document -- that Iraq could deploy chemical or biological weapons in just 45 minutes -- was inserted at Downing Street's behest despite reservations among intelligence chiefs.

Some anti-war lawmakers and political analysts have alleged that Alastair Campbell, who as director of communications at Downing Street is one of Blair's closest and most powerful aides, was responsible for that addition.

But at a reception Wednesday with foreign correspondents in London, Campbell said it was "completely untrue" that the 45-minute claim had been put in to "sex up" the dossier, and he defended its accuracy.

Though it was prepared by the Joint Intelligence Committee, "it was absolutely right and proper that Number 10 (Downing Street, Blair's office) be involved in every stage of its production," he said.

"We were, and we make no apology for that."

But he said it was "completely untrue" that the 45-minute reference was put in to "sex up" the dossier, which Blair put before parliament to reinforce his case for military action against Saddam Hussein's regime.

"That document was thorough, proper piece of work, totally authorised by the Joint Intelligence Committee, and accurate according to our best intelligence assessment," he said.

The Joint Intelligence Committee brings together the heads of Britain's intelligence agencies, and reports directly to the prime minister.

Campbell dismissed a furore over a second dossier, released by the government in February, on Saddam's efforts to conceal his development of weapons of mass destruction, which included a section lifted wholesale from a US student's thesis from the Internet.

"The only mistake that was made in relation to us was not actually to say where all that material came from," he said, adding that had been "a quite minor error by an official" which was blown "totally out of proportion."

Campbell added: "I do not accept that the 'dodgy dossier,' so-called, caused the conflict in Iraq. The conflict in Iraq was caused by Saddam Hussein and his refusal to disarm."

WAR.WIRE