London mayor Boris Johnson has said that "in all probability" he will seek to stand for Parliament in next year's general election.
"I have not got any particular seat lined-up but I do think... in all probability I will try to find somewhere to stand in 2015," he said during a question-and-answer session following a speech in London.
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He added: "It's highly likely I will be unsuccessful in that venture."
Mr Johnson said that he intended to serve out his full term as mayor which runs to 2016.
Mr Johnson said people should "never underestimate the possibility of this going badly wrong - I will try".
Asked if his target seat would be within the M25 or in a constituency in the north of England, he said: "This is a matter for the (local Conservative) association. I am not going to presume to talk about which seat I might go for."
Mr Johnson's declaration that he intends to find a seat finally puts an end to months of speculation about his ambitions to make a return to Parliament.
It immediately raised the prospect that he could emerge as a challenger to David Cameron if the Conservatives are defeated or again fail to secure an overall Commons majority.
His announcement came at the end of a speech in which he raised the prospect that Britain could leave the European Union if Mr Cameron fails to achieve his promised reforms.
Mr Cameron was quick to welcome the announcement, writing 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."
Mr Johnson acknowledged that he had been keeping people guessing about his intentions for some time.
"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.
"It's highly likely I will be unsuccessful in that venture. You should never underestimate the possibility of things going badly wrong but I will try that.
"But one thing that is absolutely clear, I will serve out my mandate here in London."
Asked if he wanted to return to Parliament so he could one day stand as Tory leader, Mr Johnson said: "No, what I said was - I don't want to revert to the kind of weasel mode here - what I said was we've got party conference coming up in almost two months time exactly.
"I don't think we're going to have this thing go on endlessly ... I've said what I have to say on that. It may all go wrong but I think the likelihood is I am going to have to give it a crack..."
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."
Bookmakers Ladbrokes responded to the news by slashing the odds of Mr Johnson becoming the next Conservative leader from 5/1 to 9/4, while his odds of becoming the next prime minister have been halved to 5/1.
Reacting to the news following his speech in Westminster, Culture Secretary Sajid Javid said: "I think it's fantastic news, he's a huge asset for London at the moment, he's been a huge asset for the Conservative Party and if he actually does get elected in 2015, he'll be a huge asset for the country.
"So I think it's fantastic news, in fact just on my way here I just texted him right away to welcome the news and I know the Prime Minister will be absolutely delighted with this news."
Asked if he would like to see him round the Cabinet table, he added: "I'd like to see him back in Parliament, but given his talents, I think once he is in Parliament, there's clearly a big role he can play."