'This is my time, says Harman in leader bid'

Gordon Brown today faced a threat of ministerial resignations and a claim that deputy leader Harriet Harman is preparing to stand for Prime Minister.

Up to 10 ministers are ready to resign if necessary to oust Mr Brown, according to one former minister who spoke to the Evening Standard.

The MP described Mr Brown as "an unmitigated failure" and went on: "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."

In another bombshell, The Times website this afternoon reported that Ms Harman is so convinced Mr Brown cannot survive that she is putting together a campaign to become his successor.

She was said to have stated "this is my time" over the weekend when reports were rife that Mr Brown will face a serious attempt to drive him from No 10 in September. Ms Harman quickly issued an emphatic denial that she had said the words or been in any way disloyal. But she would not rule herself out of a future leadership contest.

David Miliband is also widely said to be preparing the ground for a leadership election. There is talk of him standing on a "dream ticket" with Health Secretary Alan Johnson.

The developments significantly raised the danger level for the Prime Minister, although his supporters insist that talk of a challenge is down to a small minorityof disgruntled backbenchers. "I think most people have accepted that it is over and only a handful of people in Downing Street are trying to stop anything happening," a government source quoted by The Times said.

It said Ms Harman's private speech to the National Policy Forum in Warwick on Saturday night was seen as a bid for the leadership and that she was working on the unions to get support.

In an angry rebuttal, Ms Harman told the Standard: "I'm not preparing the ground for a leadership election. I have not been quietly working on the unions - I have been working with the unions on equality issues and building support for the Labour Party."

Asked if she would rule herself out of a future contest, Ms Harman replied: "There is no leadership election."

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, and the persuasive and street-wise Health Secretary could encourage 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 Jack Straw is waiting until September to advise the PM on the state of his support. Mr Miliband is said to be willing to run for the leadership - but friends say he will not move until someone else pushes Mr Brown out.