David Kay, the postwar weapons inspector whose declaration in January that Iraq had no WMD initiated a series of hammer-blows to the credibility of the Bush administration and the British government, described Mr Powell's use of Curveball's information before the UN as "disingenuous".

He told the LA Times: "If Powell had said to the Security Council: 'It's one source, we never actually talked to him, and we don't know his name', I think people would have laughed us out of court."

Mr Powell told the world on 5 February last year the administration had "firsthand descriptions of biological weapons factories on wheels and on rails" capable of producing enough anthrax or botulinum toxin to kill "thousands upon thousands of people". He showed "highly detailed and extremely accurate" diagrams of how the trucks were configured. Revealingly, he could only produce artist renditions, not actual blueprints or photographs.

Since the Powell speech, Curveball's reliability has been destroyed. The German foreign intelligence service, the BND, later warned the CIA that it had "various problems with the source". Curveball also lied about his academic credentials and omitted to tell his interlocutors he had been fired as a chemical engineer for the Iraqi army and jailed for embezzlement before fleeing Iraq in the late 1990s.

The possible existence of mobile labs was touted as a theory by UN weapons inspectors frustrated in 1992 at their failure to find evidence of chemical and biological weapons programs. (Saddam's son-in-law, Hussein Kamal, later defected and said they had been destroyed in 1991.) The UN inspectors approached Mr Chalabi for help in establishing the existence of the mobile labs in late 1997. Scott Ritter, one of the inspectors, told the LA Times: "We got hand-drawn maps, handwritten statements and other stuff. It looked good. But nothing panned out. Most of it just regurgitated what we'd given them. And the data that was new never checked out."

Evidence, much of it tentative, trickled in throughout the 1990s that Saddam may have built mobile labs to conceal his weapons programs. In 1994 Israeli military intelligence indicated that poisons were being made in red and white ice cream trucks and in green moving vans labeled"Sajida Transport" after Saddam's wife. UN inspectors later concluded this information was bogus.

The role of Israeli intelligence in the case for war was the subject of a parliamentary report released in Jerusalem yesterday. An eight-month inquiry resisted the notion that Iraq's weapons of mass destruction did not exist, but lambasted the intelligence agencies for exaggerating Iraqi capabilities, particularly before the war.

Yuval Steinitz, the parliamentarian who led the inquiry, said: "Why didn't we succeed in laying down a broad and deep framework so we could rely on reports and not speculation? That is the central question."

Much the same has been said in the US by veteran intelligence professionals appalled by their government's manipulation of information and Mr Powell's UN speech. Mr Powell is likely to come under the closest scrutiny because he was the member of the Bush administration most trusted internationally and because his presentation seemed so convincing.

In addition to the mobile labs, Mr Powell showed slides of what he said were chemical munitions facilities surrounded by "decontamination vehicles". The "chemical munitions" works were later identified by Mr Ritter and others as a site well-known to UN inspectors. The vehicles were later shown to have been fire engines.

Mr Powell also showed surveillance footage of an Iraq plane dropping simulated anthrax in what he said was a military exercise. It later emerged the plane was destroyed in 1991.

© 2003 Independent Digital (UK) Ltd