Tony Blair's former senior diplomatic adviser on Europe has accused the Prime Minister, and George Bush, of acting illegally over the war on Iraq.
In a speech last night, Sir Stephen Wall, who served under Baroness Thatcher, John Major and Mr Blair before leaving Downing Street this year, questioned the Prime Minister's judgement and accused him of "departing from the rule of law".
The timing of Sir Stephen's remarks, as the battle for Fallujah begins, were seen as highly damaging for Mr Blair, who faced criticism yesterday for committing British troops to support the assault. Sir Stephen, well-known for his pro-European views, is widely respected in the diplomatic community.
One source said: "He is an ultra-loyalist mandarin. It is astonishing that he has done this." His comments also raised further questions about the number of senior civil servants who privately believed the war to be illegal.
Sir Stephen, speaking at Chatham House, formerly known as the Royal Institute of International Affairs, said it should have been possible for a common European view on Iraq to have been reached before Britain became committed to an "unstoppable course of action" by the United States.
"I believe that in Britain we allowed our judgement of the direct consequences of inaction to override our judgement of the even more dire consequences of departing from the rule of law," he said.
In a sideswipe at Mr Blair, he added that to portray the choice as between effective action American-style, and inaction European or UN-style, was a caricature.
Downing Street played down the remarks, saying: "Sir Stephen Wall is entitled to his opinion. This was not his area of responsibility when he worked for the Government."
Last week, Kofi Annan, the UN secretary general, made an appeal for the Fallujah attack to be avoided. Mr Annan has also said the war was illegal.
Mr Blair rejected the UN letter calling for caution, when he was challenged about it by Labour MPs and Charles Kennedy, the Liberal Democrat leader