On that issue, and on her written warnings of a “humanitarian catastrophe” in the invasion’s wake, she said that Mr. Blair had effectively circumvented cabinet debate. Instead, she said, he had relied on an inner circle of “his mates” in government, having “little chats” with outsiders like herself and plying what she called a “poodle-like” relationship with the United States.

She also accused Mr. Blair of deceit in his argument shortly before the invasion that France had said that it would veto a so-called “second resolution” in the United Nations Security Council approving military action against Iraq, and that it would not shift from that position under any circumstances. That allowed Mr. Blair to say he had exhausted the diplomatic possibilities for dealing with Mr. Hussein and cleared the way for fulfilling his pledge to fight at America’s side.

“That was, in my view, a deliberate lie,” Ms. Short said. “It was one of the big deceits.” She said the truth was that that the French president at the time, Jacques Chirac, could have been persuaded to back military action if London and Washington had been prepared to give United Nations weapons inspectors in Iraq more time. “There was no emergency; no one had attacked anyone,” she said.

“There wasn’t any new W.M.D,” she added, referring to weapons of mass destruction. “We could have taken the time and got it right.”

There was little surprise in Ms. Short’s bitterness toward Mr. Blair, whose relations with the former minister had long been strained by her role as a left-wing firebrand within the governing Labour Party. The more damaging element in her testimony might prove to be her revelations about the equivocal role played in the approach to the war by Mr. Blair’s successor as prime minister, Gordon Brown, who was then Britain’s finance minister and deeply estranged from Mr. Blair.