Cook said that he believed that Blair had acknowledged that Iraq had no "usable" weapons of mass destruction just two weeks before the conflict and that there was near mutiny in the cabinet when it first discussed military action in Iraq — a claim that suggests greater opposition to the plan than has been acknowledged by the government.
In extracts from his diaries published in The Sunday Times newspaper, Cook also said that Blair "deliberately crafted suggestive phrasing" to mislead the public into thinking there was a link between Iraq and al Qaeda.
Cook said he was most concerned with a conversation he had with Blair on March 5 — two weeks before Britain went to war. At the time, the government was still trying to get a fresh UN resolution to approve the conflict and Cook was still in government as leader of the House of Commons.
Cook said he told Blair that briefings he had received made it clear that Saddam had no weapons of mass destruction "in a sense of weapons that could strike at strategic cities" and asked the prime minister if he was concerned that the Iraqi leader would use chemical munitions against British troops.
Cook said that Blair's response was: "Yes, but all the effort he has had to put into concealment makes it difficult for him to assemble them quickly for use."
Cook writes in his diary, to be published in book form as "Point of Departure," that he was deeply troubled by two elements of the exchange.
"The first was that the timetable to war was plainly not driven by the progress of the UN weapons inspections. Tony made no attempt to pretend that what (former chief UN weapons inspector) Hans Blix might report would make any difference to the countdown to invasion," he writes in a March 5 entry.
"The second troubling element to our conversation was that Tony did not try to argue me out of the view that Saddam did not have real weapons of mass destruction that were designed for strategic use against city populations and capable of being delivered with reliability over long distances."
Cook said he had also expressed that view to John Scarlett, chairman of the Joint Intelligence Committee, and that Scarlett had similarly failed to correct him.
Blair's government made the threat of Iraqi weapons the heart of its case for military action, and the prime minister has been on the defensive because coalition forces have not found such weapons.
Blair's office at Downing St. shrugged off the claims.
"The idea that the prime minister ever said that Saddam Hussein didn't have weapons of mass destruction is absurd," a spokesman said on condition of anonymity. "His views have been consistent throughout, both publicly and privately, as his cabinet colleagues know.
In the first memoir from a member of Blair's cabinet, Cook also writes that Blair was "far too clever" to allege there was a real link between Saddam and al Qaeda.
"But he deliberately crafted a suggestive phrasing which in the minds of many views must have created an impression, and was designed to create the impression, that British troops were going to Iraq to fight a threat from al Qaeda," he wrote in a Feb. 6 entry.