Harriet Harman pitches for 'stand-in' Prime Minister job if Brown is forced out

Harriet Harman is campaigning to promote herself as a stand-in Prime Minister should Mr Brown be forced out.

It emerged last night that Labour MPs have been sounded out about her suitability if the PM leaves No10 by the end of the year.

With the Prime Minister's position looking precarious, manoeuvring to replace him is well under way.

The revelation that his own deputy fancies her chances will annoy Mr Brown, who is desperate to dampen speculation about his future.

The Daily Mail understands that MPs acting on Miss Harman's behalf have approached backbenchers in recent weeks to test her popularity as a possible leader.

They are emphasising her English middle-class roots to capitalise on fears among some MPs that Mr Brown's Scottishness is contributing to his sinking popularity.

And ministers claim Miss Harman has held talks with Justice Secretary Jack Straw to enlist his support.

The lobbying is being done in private in the Commons but several MPs who have been approached say it is intensifying.

'It is discreet but the clear aim is to talk up Harriet's prospects as Labour leader in case things get bad for Gordon,' one said.

The public school-educated feminist has been quietly trading on her victory in last year's contest for the deputy leadership.

A fortnight ago she caused an uproar by championing an Equality Bill that will allow discrimination in favour of women and minority employees and require companies to publish details of the salary gap between male and female workers.

At Westminster the Bill was seen in part as an attempt to burnish her credentials with party activists who will have a key role in deciding the next leader.

Some supporters of the Prime Minister say she could emerge as a choice for what is being described as the 'anybody but David Miliband camp'.

The Foreign Secretary is favoured by some as the obvious alternative to Mr Brown, and many are urging him to show his hand.

The leadership is being discussed by all Labour MPs as they contemplate the prospect of a catastrophic general election defeat under Mr Brown. There is growing speculation that the Prime Minister might not survive the party conference season in the autumn.

But one factor protecting Mr Brown is the absence of an obvious candidate to succeed him.

Health Secretary Alan Johnson remains a favourite but has ruled himself out, while Mr Straw is seen by some as a caretaker leader.

Some MPs are championing Work and Pensions Secretary James Purnell as a standard bearer for a new generation.

With Scotland causing increasing problems for Mr Brown, some MPs are calling for a more overtly English leadership to take on Tory leader David Cameron's appeal.

Mr Straw, who has called for a greater recognition of English concerns about the consequences of giving Scotland its own parliament, is seen by some of Miss Harman's supporters as a natural ally and possible deputy on a 'dream ticket'.

But Miss Harman will have to get past large numbers of MPs in the party who fear she is too middle class to win support with the voters.