A clarion call for Britain to make its influence tell

The Foreign Office Office had an inkling last week that an unusually critical letter on British Middle East policy was on its way from a large number of ex-ambassadors. But it is unlikely to have realised just how stinging it would be.

Not since 1979, when Sir Nico Henderson sent a devastating portrait of Britain's declining influence in a leaked farewell telegram from the Paris embassy, have diplomats produced so brutally undiplomatic a critique of the government of the day. And this, unlike Sir Nico's dispatch, was intended for public consumption.

There are two probabilities about what will happen in the aftermath. One will be a contention from some loyalist government circles that the letter is over-influenced by the "camels", as the Foreign Office's Arabists are known by their detractors. The second is that the letter will strike an immediate chord among many independent-minded Middle East experts, including some currently serving in significant jobs in the Foreign Office.

The "camels" taunt anyway falls wide of the mark. Men with long and distinguished service to Tory governments as well as Labour ones, such as Sir Bryan Cartledge, the former ambassador to Moscow, Sir Marrack Goulding, former UN deputy secretary general for peace-keeping, and Sir Crispin Tickell, former ambassador to the UN, are pretty well immune to the charge.

The letter is at its most urgent on Iraq: in the pointed sentence on the total lack of a post-invasion policy, and its call on Tony Blair to stop supporting the US if Washington cannot be persuaded to conduct itself as the former ambassadors believe it should. But it is equally telling on the issue of the Israel-Palelstine conflict, where the letter's signatories have clearly been appalled to see Tony Blair standing without dissent side by side with President Bush in the week that the long-standing claim of the US to be a neutral broker seems so brusquely to have been pushed aside.

Most people who have discussed it with the Prime Minister accept that he is genuine about wanting to see peace process worthy of the name and that he understands ­ rather better, perhaps, than President Bush ­ its centrality to wider progress in the region, as well as in the "war against terrorism". Anyone who travelled with him on any of the diplomatic tours he made after 11 September attacks, remembers him making clear ­ to paraphrase him from a different context ­ that it was necessary to be "tough on terrorism, tough on the causes of terrorism".

Which is why he must surely have been deeply uneasy about the President's agreement to the punishing terms exacted from Mr Bush at his Washington meeting on 14 April by the Israeli premier, Ariel Sharon, "in return" for his plan to disengage from Gaza . They included, after all, acceptance that large Israeli settlements in the West Bank ­ settlements which the ex-diplomats bluntly describe as illegal ­ would remain Israel's after any final peace deal.

At least one well-sourced report in Israel suggested that Mr Blair was among several international leaders who privately cautioned Mr Bush against anything which would be seen as pre-empting "final status" negotiations. If so, he failed.

The bitter disappointment reflected in the letter is therefore that he has so signally failed to stick publicly by his own better judgement. By putting the best gloss on the Bush-Sharon accord, Mr Blair has already drawn a not very oblique rebuke from the European external affairs commissioner, Chris Patten. Without naming Mr Blair, and while welcoming in its unqualified form the plan to disengage from Gaza, Mr Patten said in a speech last week: "Some of course always see a glass as half full when others believe it is half empty. Others find it rather challenging to believe that a glass is half full when they can't see very much liquid in the glass at all."

For Mr Blair, of course, this is a matter of his chosen form of statecraft: that is better always to agree with the US President in public if you are to influence him in private. But the more indications there are that such influence is waning, the less easy that argument is to sustain. Mr Blair might look eastwards for some copybook lessons in how other allies sometimes treat their good friends in the United States.

Just before Ariel Sharon was due to leave for Washington for the 14 April meeting he threatened to cancel his trip until he was sure he was going to get most of what he wanted. Conversely King Abdullah of Jordan, in the wake of the Bush-Sharon accord has cancelled his own planned trip to Washington. Mr Blair may have less traction in an election year among US voters than Mr Sharon, but he has a good deal more than King Abdullah, and much more, thanks to his staunch support since 11 September 2001, than most previous British prime ministers.

The letter from the ex-diplomats is a clarion call for him to start exploiting it in the interests of Britain, the Middle East, and in the long run the US itself.