After appealing to voters to elect him for one last time, Mr Blair went as close as he could to anointing Gordon Brown as his successor. He said that at the next election Labour would be the progressive force that it had been for the past ten years whoever led it.

He added that if Labour won on May 5 it would, by the end of its next term, have made its changes irreversible, forcing the Conservatives to change their approach if they were to win again. Labour would have achieved a “settlement” as important as that after 1945 when all parties accepted the health service and the welfare state.

Labour highlighted more than 270 pledges in its election manifesto, though a vast number have appeared in five-year plans published over recent months.

Among new promises were to build a new generation of NHS community hospitals, state-of-the-art centres to provide diagnostics, day surgery and out-patient facilities; making all secondary schools independent specialist schools and allowing good primary schools to become foundation schools; new measures to tackle anti- social behaviour, including allowing victims to give evidence anonymously; expansion of the M1 and M6 motorways and studies for a national system of road pricing.

Mr Blair warmed to his theme of Labour keeping its grip on power as he hit the campaign trail with John Prescott. He said that if the party succeeded in embedding its “progressive consensus” it could “keep on governing — governing with the support of our country, governing because we had the courage to make the changes that made this a Government that can run the economy well, invest in public services and create a fairer country”.

Mr Blair and Mr Brown appeared to be sealing an open pact — one aide called it a “public Granita”, in reference to the deal that the two were alleged to have made about the leadership in 1994. Mr Brown has been happy to agree to what Mr Blair called a quintessentially new Labour manifesto.

By being bound into what some were calling a “treaty of succession”, Mr Brown is an even stronger favourite to replace Mr Blair than he was only a fortnight ago. Mr Blair has told friends privately that Mr Brown accepts that the new Labour approach is the way to win in 2009-10.

The Times has been told that Mr Brown secured changes to the manifesto that gave a stronger emphasis to the “opportunity economy” and that he ensured that all promises were funded, but that he had not demanded any deletions. In returning to the centre of the campaign, his main prize was to have put the economy and the contrast with the Tories at its heart. Yesterday he lavished praise on Mr Blair at every opportunity, calling him a “great Prime Minister” and the “most successful leader Labour and the country has had”.

But, as Mr Brown promised that Labour would not raise tax rates in the next Parliament, while leaving open the possibility of a national insurance rise, Labour’s manifesto launch was jolted by the intervention of the International Monetary Fund, which warned him that he would have to rein in spending or put up taxes. The IMF told him to hasten the pace of “fiscal consolidation” or cut borrowing to meet his fiscal rules.

Michael Howard called the report a “tax bombshell” although the Conservative attack on Labour’s tax plans was blunted by their own admission that they could not rule out tax rises. Mr Brown said that the IMF had got it wrong.

Mr Brown swiftly stamped on the idea that a national insurance rise might be needed to fund big pension reforms in the next Parliament. He made plain that if an official report by Adair Turner, the former head of the CBI, proposed compulsory second pensions, there would be a lengthy debate. That would take longer than the next Parliament.

Mr Blair and Mr Brown dominated the manifesto launch in an attempt to contrast Labour’s team approach with a Conservative campaign in which they claim that Mr Howard is a “one-man band.”

With Mr Blair on stage at the Mermaid Theatre in London was the whole of his Cabinet. Six of them — Mr Brown, Mr Prescott, Charles Clarke, John Reid, Ruth Kelly and Patricia Hewitt — took turns to read from one single statement.

The manifesto said that House of Lords reform is to be completed by abolishing the remaining 92 hereditary peers and a free vote among MPs on how the Upper Chamber should be composed. Mr Blair has not dropped his opposition to a part-elected, part-nominated House, but appears ready to accept the decision of MPs.

Mr Blair’s declaration that his legacy was safe came at the end of the launch. He said: “I have said this is my last election. At the election following, there will be a different leader. What this manifesto shows is that when at that election this party is under new leadership, it will continue to be the modern, progressive Labour Party of the last ten years.”

Mr Blair promised to campaign for a “yes” vote in the referendum on the European constitution but he said that he would use the veto to protect Britain’s budget rebate.

Mr Howard said Labour’s promises would never happen and accused Mr Blair of having lost the plot: “It’s no use making all these promises now. He’s had eight years. They’ve heard it all before,” he said.

Sir Menzies Campbell, for the Liberal Democrats, said: “All the promises and all the pledges in this manifesto will not cure the profound sense of distrust so many people have about Labour.”

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