The prime minister has come under attack from Michael Howard and Robin Cook as the row over Iraq's weapons of mass destruction continues.

The Tory leader seized on Tony Blair's admission that when he asked the Commons to back war last March he had not known that the now-infamous claim about weapons being deployed within 45 minutes applied only to battlefield munitions.

Michael Howard suggested this was a “grave dereliction of duty” that should make the prime minister consider his position.

Robin Cook, who was in the Cabinet until shortly before the war vote, repeated that he knew which weapons the claim referred to and it was “hard to credit” that intelligence chiefs did not tell Tony Blair.

Defence secretary Geoff Hoon has also come under fire in the media for saying that the 45 minute issue was "not a matter of great public concern" when the intelligence dossier was published.

Meanwhile, in Washington, George Tenet, director of the Central Intelligence Agency, said that US intelligence had never claimed Iraq posed an “imminent threat”.