Ten ministers ready to quit

The bombshell threat means the Prime Minister could face a mass resignation before Labour's conference in September.

The danger level to Mr Brown also increased following reports that David Miliband and Alan Johnson are being urged to forge a "dream ticket" in any leadership contest.

A former minister told the Evening Standard: "Brown is proving an unmitigated failure and there is no shortage of MPs who are willing to go public with that view.

"I have spoken to several members of the Government who say they will resign if it proves necessary to provoke a change of leader before it is too late. There are probably at least 10.

"There are other MPs, like me, who will sign a letter asking the Prime Minister to stand down. We cannot go on to the general election with the Government in such a hopeless state.

"We know there are candidates who would be an improvement, such as David Miliband or Jack Straw." Both developments significantly increase the possibility of a bloody attempt to drive the Prime Minister from office, a step that Labour rebels hope can be avoided by Mr Brown agreeing to go quietly.

Until now there has been no obvious successor for disenchanted Labour MPs to rally around but the suggestion of a pairing between Mr Miliband, the young and cerebral Foreign Secretary, with the persuasive and street-wise Health Secretary, Mr Johnson, could encourage the rebels. There is no suggestion that either man has agreed to a formal pact but a Labour grandee said: "It is still very early but a Miliband-Johnson ticket is one option being spoken-about." Justice Secretary Mr Straw is waiting until September before assessing the state of the party and the opinion polls and deciding whether to approach Mr Brown and urge him to go.

Mr Miliband is ready and willing to run for the leadership - but his friends say he will not move until someone else pushes Mr Brown out.

Former minister George Howarth is collecting names for a letter to the Cabinet from MPs wanting a change of leader - a move that would massively destabilise Mr Brown's position.

The idea of a walkout of ministers is a nuclear option that echoes the brutal "September Coup", when a leaked letter from disenchanted MPs and a series of staged resignations were engineered to cause a crisis. It succeeded in forcing Tony Blair to announce a firm retirement date.

Guardian columnist Polly Toynbee called on Mr Brown to quit saying: "I personally think that for the survival of the Labour Party, he has to go."

Mr Brown's supporters say there would be "unstoppable" pressure for an early general election if Labour changed leader for a second time since 2005.