Tony Blair was facing a severe crisis of confidence in his foreign policy yesterday after an unprecedented attack from dozens of the most senior figures in the British diplomatic service.
The letter from 52 former ambassadors and heads of mission who held the most senior postings in the Foreign Office, lambasted Mr Blair for abandoning his principles over the road-map to peace in the Middle East and criticised the United States-led coalition in Iraq for failing to plan for the post-Saddam era.
In a damning verdict on Mr Blair's special relationship with President George Bush, they called for a "fundamental reassessment" of British policy towards the White House and the Middle East, urging Mr Blair to exert real influence over American policy as "a matter of the highest urgency".
They added: "If that is unacceptable or unwelcome there is no case for supporting policies which are doomed to failure."
Signatories include former ambassadors to Baghdad and Tel Aviv, and senior figures who served in postings including Moscow, Brussels and the United Nations. Downing Street said that Mr Blair would reply in due course, but Labour critics seized on the diplomats' intervention as evidence that Britain was too close to the White House.
Oliver Miles, a former ambassador to Greece and Libya who helped co-ordinate the letter, said: "A number of us felt that our opinions on the two subjects, Iraq and the Arab-Israel problem, were pretty widely shared and we felt that we ought to make it public.
"Never has government policy been so controversial. It is an indication of our serious concern that what is probably the biggest such collective group has gone straight to government in this way.
"Our objective is not to damage Blair politically but to strengthen the hand of those who feel as we do."