TONY BLAIR’S growing isolation was laid bare last night, when it emerged that he ditched his deeply unpopular policy on Lebanon after a “devastating” letter from his most trusted ambassador.

The Times has learnt that the Prime Minister softened his hardline stance on the Lebanon war after Sir David Manning, Britain’s Ambassador to Washington, sent him an impassioned letter bemoaning the failure of British policy.

Mr Blair was under further attack yesterday as normally loyal MPs, including senior backbenchers and ex-ministers, unleashed a torrent of public criticism after he told The Times that he would not set a timetable for leaving No 10.

Andrew Smith, the former Work and Pensions Secretary, said: “I would have thought it’s clear to everyone that the debilitating uncertainty over the leadership can’t go on — it’s bad for the country, bad for the Government, bad for the Labour Party and, ultimately, bad for Tony Blair himself.”

Last night the Foreign Office threatened to seek an injunction against The Times if it published Sir David’s letter, but no further contact was made.

As the Middle East conflict intensified in July, Mr Blair was already under fire from Cabinet colleagues and the media. But sources said that the hardest hitting criticism came from Sir David. “It had a huge impact in Downing Street,” one source said. “It was as candid as the letter by the outgoing Ambassador to Baghdad [William Patey]” who had given warning of civil war in Iraq.

After the letter from Sir David, Mr Blair shifted quickly from solid support of President Bush, and a refusal to call for an immediate ceasefire in the fighting, to calling openly for an urgent ceasefire. Mr Blair hopes now to rehabilitate his damaged reputation at home and abroad by launching a peace mission to the Middle East next weekend, in time to face his critics at the Labour Party conference on September 24.

Sir David is more than just Britain’s most senior envoy, with close relations to Condoleezza Rice, the US Secretary of State. He was Mr Blair’s top foreign policy adviser over 9/11 and through the Afghanistan and Iraq wars. Previously he was Ambassador to Tel Aviv.

In the first two weeks of the Lebanon war Britain mirrored US policy, insisting that it would be pointless to demand an end to the fighting until a mechanism was in place to keep the peace. In the region this approach was regarded widely as allowing Israel a free hand to step up its assault on Hezbollah and destroy Lebanon’s infrastructure.

Mr Blair was keenly aware of the damage being done to his international standing. Nevertheless he reiterated the policy side by side with President Bush on July 28 at the White House, when the two men refused pointedly to call for a immediate ceasefire.

But according to British diplomats, Sir David then made a second attempt. This time the two men spoke alone and at length as Mr Blair travelled to California for public engagements without his normal No 10 retinue. “The Downing Street aides went home leaving Manning to work on Blair,” a British official said. “Manning urged Blair to be more robust in calling for a ceasefire and criticising US policy.”

Britain, which has never played a leading role in Lebanese affairs, was being damaged unnecessarily. Also, Sir David feared that the conflict could grow and that hardliners in the Bush Administration could push Israel to extend its campaign to Syria. Mr Blair was told he must bolster the position of Dr Rice and moderates at the State Department.

The result was dramatic. On July 30 Mr Blair called for “an urgent cessation of hostilities” and spoke about the need for a new peace initiative. Two days later at the Los Angeles World Affairs Council he called for a “complete renaissance” of foreign policy. He said that the battle against militant Islam could not be won by force alone.

Today Mr Blair privately concedes that he has been damaged by his stand on the war in Lebanon, but believes that he can salvage his reputation. Next Saturday Mr Blair travels to the Middle East when he hopes to revive the peace process.

Times Recommends

• Everyone will get vaccine against swine flu
• Artificial sperm and the race to build a baby
• BBC jets out stars to tout for prizes