Mr Bryant, who has repeatedly been passed over for a ministerial job, read the interview with The Times last Friday in which Tony Blair refused even to contemplate setting a date for his departure.

Mr Bryant, 44, who held Rhondda at the last election with a majority of more than 16,000, was so incensed that he telephoned Siôn Simon, 37, the MP for Birmingham Erdington, who is his closest friend in the parliamentary party.

The two men were among the brightest of the 2001 intake but complain privately that they have been denied ministerial office because of two much publicised incidents in their private lives. Mr Simon, who has two young children, left his wife for a BBC journalist. A photograph of Mr Bryant dressed only in his underpants on a gay sex website was leaked to a Sunday newspaper.

They had decided weeks earlier that they would move against the Prime Minister if there was the right provocation. His failure to set a timetable was the signal they had been waiting for.

Mr Bryant, who had been working on a biography of the Duke of Buckingham in his secluded farmhouse high above Rhondda, had been wrestling with his conscience for some time. He decided to try to rally support among fellow MPs first elected alongside him in 2001 who, crucially, were not the usual suspects.

He took time off from his writing to phone his colleagues. By the end of the weekend, 17, more than half the 2001 intake, had either signed up or agreed to support a letter demanding that Mr Blair clarify when he intended to stand down. The initial list included one minister and a clutch of parliamentary aides, who are on the lowest rung of the ministerial ladder.

This was by no means the main revolt facing Mr Blair, but the fact that it involved loyalists hitherto loyal to the Prime Minister will have stung Downing Street.

A sign of the loss of support for the Prime Minister was underlined by the swift involvement of Kevin Brennan, a whip, who is supposed to impose discipline on his party colleagues. Another rebel is Tom Watson, a defence minister popular with his colleagues.

Mr Bryant drafted an e-mail that declared the continued support of the signatories for the new Labour project. It referred to them all as keen modernisers who were proud of their achievements since Labour came to power in 1997.

But the missive demanded clarity in the Prime Minister’s intentions and rejected his claim in The Times that they were seeking to turn back the clock.

It was read over the telephone to the proposed signatories to try to ensure that it was not leaked. Initially, it stated: “We believe that it is in the interests of clarity that you should make your intentions . . . to go now.” It was subsequently watered down to demand a detailed timetable for his departure.

The e-mail was sent by Mr Bryant to Keith Hill, the Prime Minister’s parliamentary private secretary and link to Labour MPs, on Monday afternoon. Among the signatories were Chris Mole, Ian Lucas, Khalid Mahmood, Wayne David, David Wright and Mark Tami, all parliamentary private secretaries and expected to support the Government.

Fellow MPs were quick to point out the links of some of them to Gordon Brown: Mr Tami is PPS to Dawn Primarolo, a Treasury minister, and Kevan Jones, MP for Durham North, is a keen supporter of the Chancellor.

One MP who backed the letter but declined to be named, said that a series of events had forced them to act against Mr Blair. He cited as crucial the interventions on policy of Alan Milburn and Stephen Byers, former Blairite Cabinet ministers, last month to try to ensure that any Gordon Brown succession should be tied to a Blairite programme or reform.

Significantly, Mr Bryant and Mr Simon were the loudest backbench critics of the proposal by Mr Byers for the abolition of inheritance tax. Mr Brown took great satisfaction from seeing the plan savaged by two ultra-Blairites.

It was the first public outing of the Bryant and Simon double act, which was limbering up to inflict much more serious damage on the Prime Minister himself. The pair were the subject of vicious counter-briefing yesterday, reflecting the anger within Downing Street at the turn of events.

One minister told The Times: “They are both disappointed men. Chris Bryant openly canvassed for a job in the last reshuffle and failed.”

Mr Blair’s refusal to demand an Israeli ceasefire in Lebanon was another factor in hardening opinion still further among even his closest parliamentary party supporters.

One signatory to the letter, who declined to be named, said: “The outriders, Milburn and Byers, really upset the apple cart, particularly as we know their intervention was sanctioned by Blair. If that was not bad enough, with all the Middle East stuff, then there was the interview in The Times. It was a terrible mistake. It backfired horribly, which is why so many of the payroll vote were willing to sign.”

A second letter was circulating yesterday among Labour MPs who entered the Commons last year, which colleagues said also called on Mr Blair to quit now but which had yet to be sent. Kerry McCarthy, MP for Bristol East, told the BBC that she had seen a separate letter drafted by members of the 2005 Labour intake but had not signed it herself.

Another Labour MP, Karen Buck, released a statement signed by 49 MPs declaring themselves satisfied with the timetable set out by David Miliband under which Mr Blair would quit in a year.

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