A roll-call of former British diplomats blasted Tony Blair on Monday and said it was time for the prime minister to start influencing America's "doomed" policy in the Middle East or stop backing it.
In an unprecedented letter signed by 52 former ambassadors, high commissioners and governors - the top ranks of British diplomacy - Blair was urged to sway US policy in the region as "a matter of the highest urgency".
The diplomats, among them former ambassadors to Iraq and Israel, told Blair 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.
"We feel the time has come to make our anxieties public, in the hope that they will be addressed in parliament and will lead to a fundamental reassessment," said the letter, sent to Blair on Monday and made available to Reuters.
Blair's spokesman was not immediately available to comment on the attack, which the diplomats believe is unprecedented in scope and scale.
It comes as Blair faces deep discontent among voters for backing a US-led war that most Britons had opposed and for endorsing a Washington-driven policy that has put London on collision course with allies in Europe.
The diplomatic swipe is bound to be seized upon by Blair critics as fresh evidence that British interests come second to America's because of Blair's zealous alliance with President George W. Bush and his neo-conservative agenda.
The diplomats zeroed in on two key initiatives dominated by Washington - Israeli-Palestinian peace negotiations and war in Iraq - and wrote off both as "doomed to failure".
"Never has government policy been so controversial. It is an indication of our serious concern that what is probably the biggest ever such collective group has gone straight to government in this way," the letter's co-ordinator Oliver Miles, a former ambassador to Greece, told Reuters.
"Our objective is not to damage Blair politically but to strengthen the hand of those who feel as we do," said Miles.
"Our voice will be heard."
Among the signatories are former ambassadors to Baghdad and Tel Aviv, top Arabists and non-regional specialists who served from Moscow to Brussels to the United Nations.
The career diplomats urged Blair to use his alliance with Bush to exert "real influence as a loyal ally... If that is unacceptable or unwelcome, there is no case for supporting policies which are doomed to failure."