For a few short hours yesterday, it looked like the carefully cultivated relationship between Tony Blair and George W. Bush was reaping substantial dividends.

At lunchtime, as he prepared to depart for weekend talks with the president at his Texas ranch, the prime minister called on the US to show more leadership in the Middle East. In uncharacteristically blunt language, he told Mr Bush the experience of Northern Ireland showed that only the involvement of a powerful third party could bring two warring sides together.

By teatime the president had ordered Colin Powell, secretary of state to the region, to try to get both sides back to the negotiating table.

However, closer examination of yesterday's events revealed that what first looked like payback time for standing "shoulder to shoulder" with the US, despite growing dissent at home, was more a triumph of presentation than diplomacy.

Mr Blair's words, contained in a briefing from Downing Street staff, were given the green light by the White House in extensive talks between Sir David Manning, the prime minister's foreign affairs adviser, and Condoleezza Rice, national security adviser.

Mr Blair's growing concern certainly weighed more heavily with the US administration than that of other European Union leaders. But even Mr Blair's advisers privately admitted that the escalating discomfort in the White House meant the policy of total support for Israel was running out of time.

However, President Bush's change of heart gets Mr Blair off the hook at home, in the short term at least.

Labour backbenchers have grown scornful of the friendship between the two leaders, asking what exactly blanket support for the president has secured for Britain. Rows over US withdrawal from the Kyoto protocol, the anti-ballistic missile treaty and, most recently, the imposing of tariffs on steel imports, have made Britain look powerless to influence the White House.

MPs are particularly concerned that this lack of influence means Britain will be dragged into military action in Iraq.

Against this background, Mr Blair could not afford to leave Texas empty-handed and President Bush's action allows his Downing Street staff to speak of a new golden age for the "special relationship".

For Mr Blair and New Labour, strong friendship with the White House is not negotiable.

"Do not underestimate how important the relationship with the White House is for New Labour," said one cabinet minister. "It is enormously important for the repositioning of Labour as the natural party of government that we have a very good relationship with the world's only super-power, and we are prepared to put up with a lot."

History shows the dangers of being out of step with Washington. When, in 1956, Sir Anthony Eden miscalculated that the US would not intervene in the Suez crisis, despite its obvious misgivings, it felt the full force of White House anger. President Dwight Eisenhower promptly imposed financial sanctions, pulling the rug out from under the pound.

"This was definitely the low point," said Vernon Bogdanor, professor of government at Oxford University.

"Eisenhower was standing for re-election as the man who brought peace to the world. What the UK did was cut across that programme. Macmillan [who succeeded Eden] had to spend a lot of time repairing the relationship," he added.

Neither is Mr Blair the first prime minister to face criticism at home for his friendship with a president. Harold Wilson was savaged by Labour MPs for his abject verbal support for Lyndon Johnson during the Vietnam war, although he caved in to their pressure by refusing the US request for military help.

Peter Hennessy, professor of contemporary history at Queen Mary University of London, predicts that Mr Blair may yet face more problems at home over his friendship abroad.

"There was certainly a gilded moment after September 11 but the further we get from that the more political and military difficulties present themselves," he said. But US/UK relations had firmer foundations than who happened to be in power.

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