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."
The intervention raised fresh questions over Mr Blair's foreign policy and comes as Britain considers further troop deployments to quell the ongoing violence in Iraq.
It also follows accusations against Mr Bush of ending hopes for the international road- map to peace in the Middle East by signing a unilateral Israeli peace plan.
The former diplomats said they had "watched with deepening concern the policies which you have followed on the Arab-Israel problem and Iraq, in close co-operation with the United States".
The Prime Minister's official spokesman said: "We are aware of this and we will be responding to this in due course.
"They are entitled to their views. What I would stress is that our objectives in Iraq and the Palestinian conflict remain stability, peace and freedom in the Middle East."
But many Labour MPs reacted with astonishment. Mr Bush's statement of commitment to the Middle East road- map last year was hailed by ministers and backbenchers as the most concrete evidence of Mr Blair's influence over the White House in the build up to war.
The hopes of Labour MPs and senior diplomats were dashed earlier this month when Mr Bush signed up to a unilateral peace plan put forward by the Israeli Prime Minister Ariel Sharon, which appeared to abandon key elements of the international peace plan championed by Britain.
Doug Henderson, the former defence minister, said: "These are the guys on the ground with a lot of experience of dealing with critical issues. We would be well advised to listen to their views very carefully." Tam Dalyell, the Father of the Commons, added: "I fully support the 52 diplomats. This is unprecedented. In my 41 years as an MP I have never seen such a move. They can't be dismissed as ex-diplomats, it's a great deal more serious than that."
Malcolm Savidge, the Labour MP for Aberdeen North, said: "It's very important that we distinguish between being a close ally of the US and appearing uncritically to support George Bush's administration."
The Conservatives declined to comment, but Sir Menzies Campbell, the Liberal Democrat foreign affairs spokesman, said: "This is a remarkable intervention in the debate about the Middle East from a group of people who are almost certainly the most expert in Britain on the issue. The Prime Minister would be well advised to take account of their criticisms.
"When the House of Commons was persuaded to endorse military action against Iraq it was, among other things, on the footing that the road-map would be implemented, and that the two-state solution would have priority."
But Donald Anderson, the Labour chairman of the Commons foreign affairs committee, said the former diplomats had not reflected the full picture. He said: "This is unprecedented and comes from a distinguished group of former ambassadors. But the Prime Minister did not give a total endorsement of the Israeli plan."
Robin Cook, the former foreign secretary, backed the diplomats. He told Channel 4: "There was a bargain offered at the time that if we supported Bush's invasion of Iraq then he would press for peace in the Middle East on the road-map. Now he has broken that commitment, instead he has taken sides with Sharon and that, I think, is what motivates the comments we see about the Middle East within this letter."
FOUR LEADING SIGNATORIES
SIR TERENCE CLARK
Britain's man at the court of Saddam Hussein between 1985 and 1989. Having been ambassador to Iraq during those years, Sir Terence had a unique insight into the dictator and his country. Also a former ambassador to Oman, Sir Terence has written a series of books on the politics, culture and dogs of the region.
Urbane Foreign Office spokesman for Geoffrey Howe. Became British trade commissioner to Hong Kong and then consul general after the handover. One of those rare birds a diplomat who knew how to handle the press. He ran the Foreign Office news department before serving as ambassador to Israel from 1998 to 2001.
SIR MARRACK GOULDING
An Arabic speaker who served in the diplomatic service in Kuwait, Libya, Egypt and Lebanon, Mr Goulding also worked for the UN Secretariat for seven years; he ran the vast peacekeeping division. During that period, from 1986 to 1993, he oversaw operations in Namibia, Cambodia, Angola, Mozambique, El Salvador and the former Yugoslavia.
Entered the diplomatic service in 1960 after graduating in Oriental studies from Oxford. He was ambassador to Libya when WPC Yvonne Fletcher was killed in 1984, when he was besieged in the embassy by unofficial militia. He later became ambassador to Greece and Luxembourg and has been a business consultant since retiring in 1997.