Boris plans Westminster return as bookies slash odds on him leading Tories

Prime Minister David Cameron was quick to welcome the announcement, saying that he had always wanted to see “my star players on the pitch” during the forthcoming election campaign.

However Mr Johnson’s declaration immediately raised the prospect that he could emerge as a rival for the Conservative leadership if the party is defeated - or again fails to secure an overall Commons majority - at the polls.

Bookmakers Ladbrokes responded by slashing the odds of Mr Johnson becoming the next Conservative leader from 5/1 to 9/4, while Labour said it was a clear sign the Tories were turning in on themselves with Mr Cameron powerless to intervene.

The mayor provocatively used a question-and-answer session at the end of a speech in which he highlighted the “attractive” prospects for Britain outside the European Union if Mr Cameron fails to secure his promised reforms.

“I think we’ve danced around it an awfully long time now, and as you know the Prime Minister ages ago said he would welcome me back - very kind of him to say so - and has also been pretty clear that I can’t endlessly go on dodging these questions as I’ve tried to do,” he said.

“So, let me put it this way - I have not got any particular seat lined up but I do think in all probability - since you can’t do these things furtively, I might as well be absolutely clear - in all probability I will try to find somewhere to stand in 2015.”

While he added that it was “highly likely” that he would be unsuccessful in his search for a seat, few at Westminster doubt that his announcement will see him return to the centre stage of British politics.

Mr Cameron, currently holidaying in Portugal, wrote on his Twitter feed: “Great news that Boris plans to stand at next year’s general election - I’ve always said I want my star players on the pitch.”

Nevertheless, the news will be greeted with mixed feelings in Downing Street. While Mr Johnson’s undoubted popular appeal will be an electoral asset, his return to Westminster will galvanise Euro-sceptic Tory MPs determined to secure Britain’s exit from the EU.

For Labour Sadiq Khan, the shadow minister for London, said Mr Johnson’s announcement showed the Conservatives were turning in on themselves.

“Boris Johnson’s announcement reveals how weak David Cameron is and how out of touch the Tories remain,” he said.

“Rather than focusing on helping the millions of Britons suffering from the cost-of-living crisis, the Tories are increasingly turning inwards, focused on leadership battles to come, with David Cameron powerless to do anything about it.”

Mr Johnson refused to say whether he had discussed his plans with Mr Cameron, although he said that it was said it was largely at the Prime Minister’s instigation that he decided to “have a crack”.

“My conversations with the Prime Minister are many and various and I don’t propose to go into them,” he said.

Mr Johnson sought to sidestep questions about his leadership ambitions, insisting that he wanted to continue supporting Mr Cameron who he described as a “brilliant” Prime Minister.

He made clear however that he would relish the prospect of ministerial office once he has completed his term as mayor which runs to 2016.

“I would like to see if I could be useful again in Westminster, because when I was there last time after all we were in opposition and I spent quite a lot of the time bashing away at Tony Blair and Gordon Brown and pretty miserable it was,” he said.

“I’d love to see what it’s like in government.”

Mr Johnson refused to be drawn on where he might stand - although there is intense speculation that he could go for Uxbridge where former deputy chief whip John Randall - who is standing down - held the seat with a majority of 11,216 at the last general election.