The leader of the Commons and former foreign secretary is being talked of in Downing Street circles as Tony Blair’s preferred successor if Prescott can be persuaded to fall on his sword. His friends said he would throw his hat into the ring if the post becomes vacant.

It comes as ministers with eyes on the second most important job in government began jostling for position this weekend. Alan Johnson, the education secretary, said he would be “interested” and Peter Hain, the Northern Ireland and Wales secretary, is expected today to refuse to rule himself out.

Many MPs believed Straw was no longer a contender after he was demoted in last month’s government reshuffle, but friends of the minister insisted he was likely to run if a vacancy became available.

“I think he would relish the idea of having a go at it,” said one MP close to Straw. “He is a seasoned campaigner and good at building relationships. He’s always kept the left onside and is a good broker.”

Another source said: “His view is that there isn’t a vacancy at the moment but, if there was, it would not be remotely surprising if he put his name forward. There would be people saying he should stand.”

If pressed in public, Straw is likely simply to say that there is “no vacancy” for the post, the accepted formula used by politicians to avoid looking disloyal.

Downing Street is said to favour Straw as the “compromise candidate” who could unite all wings of the Labour party and act as an honest broker between the prime minister and Gordon Brown over the transition of power when Blair steps down, probably next year. One senior figure in No 10 said he expected Blair to go as early as May, his 10th anniversary of being in office.

A No 10 source said that should the beleaguered Prescott step down, Straw would be “the obvious choice”. A YouGov poll of Labour party members for The Sunday Times today shows only 25% think Prescott should give up now. Most, 56%, think he should stay on until Blair steps down.

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