The Government today formally withdrew its controversial claim that Iraq had had chemical and biological capable of being deployed within 45 minutes.

In a Commons statement, Jack Straw, the Foreign Secretary, disclosed that a further line of intelligence reporting on Iraqi production of biological weapons agents before the war had also now been withdrawn by John Scarlett, the head of MI6.

Mr Straw’s statement means that the Secret Intelligence Service has now had to withdraw three of its main lines of intelligence reporting on Iraq’s weapons prior to the war.

In his report on the Iraq intelligence published in July, the former Cabinet Secretary Lord Butler of Brockwell disclosed that MI6 had already withdrawn the intelligence from one of its main sources in the country as it was now considered unreliable.

The Butler report also criticised the use of the 45-minute claim in the Government’s now notorious dossier on Iraqi weapons published before the war.

It said that it was a "rare" example of the original intelligence material not being correctly reported in the assessments of the Joint Intelligence Committee - Britain’s senior intelligence body which drew up the dossier.

In the Commons, Mr Straw strongly defended the dossier and the intelligence assessments of the JIC. "That dossier accurately reflected the views of the JIC at the time that it was signed off by them," he said.

"Far from the dossier being some confection, it was based on the best judgments not just of ourselves but of the wider international community. Everybody assumed Saddam had these weapons."

The disclosure that MI6 has now withdrawn the 45-minute claim is a further embarrassment for both the Government and the Secret Intelligence Service.

The claim - which featured four times in the dossier - has become a touchstone in the ongoing controversy over the case made by Tony Blair for taking Britain to war.

It was cited in the controversial BBC radio report by Andrew Gilligan as the "classic example" of the Government having "sexed up" the dossier to strengthen the case for war.

The Parliamentary Intelligence and Security Committee subsequently criticised the dossier for failing to make clear that it referred only to battlefield weapons, and not ballistic missiles as some reports had assumed.

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