Tony Blair failed to stand up to George Bush over the invasion of Iraq, the former US secretary of state Colin Powell has claimed.
The damaging disclosure by an influential participant in the build-up to the war will undermine claims by Mr Blair's allies that he acted as a restraining influence on the president.
The observation is made in Blair Unbound, a new book about the former prime minister by the political biographer Anthony Seldon. Mr Powell recalled how he and Jack Straw, the former foreign secretary, attempted to find ways of restraining the two leaders.
At one point Mr Straw even flew to the US by Concorde to hold secret talks with his American ally.
But Mr Powell told Dr Seldon: "In the end Blair would always support the president. I found this very surprising. I never really understood why Blair seemed to be in such harmony with Bush. I thought, well, the Brits haven't been attacked on 9/11. How did he reach the point that he sees Saddam as such a threat? Jack and I would get him all pumped up about an issue. And he'd be ready to say, 'Look here, George'. But as soon as he saw the president he would lose all his steam."
In extracts from the book in The Mail on Sunday, Dr Seldon also disclosed that two of Mr Blair's most senior Downing Street advisers, Sir David Manning and Baroness Sally Morgan, argued against the war.
According to the book, Mr Blair resolved to write to Mr Bush in 2002 to spell out his fears that the momentum for war was growing too fast in America.
But he "faltered and pulled his punches" and in effect told the president: "You know, George, whatever you decide to do, I'll be with you."
Sir Christopher Meyer, Britain's former ambassador to Washington was horrified, asking Sir David: "Why in God's name has he said that again?
"'Well, we tried to stop him ... but we didn't prevail', came the weary response."
The book also claims Mr Straw was sidelined before the war and removed afterwards for not giving enough support to Mr Blair.
Dr Seldon writes that the former prime minister had private doubts about the strategy, but "as ever, Blair refrained from expressing his frustration in public" even towards the end of his days in Downing Street.
"We had been in there with him from the start and at this very late stage the Prime Minister did not want to be seen to fall out with George Bush," he is quoted as saying.Reuse content