Speculation over the ambitions of Hull West and Hessle MP Alan Johnson is growing after the shock resignation of Gordon Brown.

Mr Brown fired the starting gun for a leadership election following the Labour party's losses in the General Election.

While he continues to negotiate with the Liberal Democrats over whether the two parties can form a coalition government, Mr Brown also set in train a process that could see Mr Johnson run for the top job in British politics.

Mr Brown's successor will not only be Labour leader, but could – if talks with the Lib Dems lead to a deal – become Prime Minister.

Home Secretary Mr Johnson was locked in a meeting of senior Labour figures at Downing Street last night, and had not made a statement about his intentions by the time the Mail went to press.Unconfirmed reports suggested the favourite to succeed Mr Brown, Foreign Secretary David Miliband, had already decided to throw his hat into the ring.

But Mr Johnson is at the centre of speculation that the party will instead seek a caretaker leader to steer Labour through its present difficulties, rather than picking a member of the younger generation.

Mr Johnson has spoken repeatedly of the need to reform the UK's voting system, which is likely to be a key demand of the Lib Dems in any pact with Labour.

He refused to be drawn on his ambitions just days ago, telling the Mail: "No-one is being asked to rule themselves in or out of any scenario in the future, so I don't see why I should do that.

"It doesn't mean that I am angling or plotting."

To succeed Mr Brown, Mr Johnson would have to win support from MPs, the party's grassroots and the unions in a three-month contest.

In 2007 he ran for deputy leader of the party under the same rules, being narrowly pipped to the post by Harriet Harman.

The MP who ran his campaign and would be expected to manage any new leadership bid, Sports Minister Gerry Sutcliffe, told the Mail he was unsure of Mr Johnson's plans.

"I'm waiting to hear from him myself," he said.

Mr Johnson received strong backing from Hull East's new Labour MP, Karl Turner.

Mr Turner, who voters picked to replace John Prescott as one of the city's representatives last week, said: "I haven't spoken to Alan about this, he's a very good friend of mine and he's been very supportive since the day I was selected.

"But he would be a superb leader of the Labour Party and if he were to throw his hat into the ring I would absolutely support Alan Johnson.

"He's very natural, he's a man who's been a normal person. He didn't go to university and then straight into politics – he was a postman.

"He's a great guy and he's very charming and charismatic.

"I think he would be very popular as a leader of the Labour party, and as Prime Minister."

Mr Turner added it was "very sad" that Mr Brown had decided to stand aside.

He said: "I think Gordon Brown has led the Labour Party very well and I think he's served the country very well.

"I suspect it's (his decision to step down) to allow the Labour Party and the Lib Dems to decide whether they can work together in a coalition."