London Mayor Boris Johnson said he did not know whether he would stand again as an MP after being repeatedly grilled about his ambitions by a caller on live radio.
There has been growing speculation that the mayor could stand for Parliament before the end of his term in 2016 and David Cameron has discussed the possibility of Mr Johnson returning to the Commons.
The Prime Minister said it would be "great" for Mr Johnson to return "at some stage", but Mr Johnson refused to be drawn on whether he would stand in the 2015 general election.
Mr Johnson joked that he would like to be a romantic novelist or play rugby for England as he sidestepped questions about his future.
Asked about his ambitions on LBC 97.3 he said: "It was very kind of the Prime Minister to say what he said and obviously I want to be as supportive as I can.
"But I've got a very big job to do and that's what I'm going to do."
But caller Tony from Woodford pressed Mr Johnson to give a "straight answer" to the question about his future ambitions.
Mr Johnson said: "I am going to stick around for as long as my mandate runs."
Asked whether he would like to become an MP the mayor replied: "I would like to play rugby for England ... this is worse than Jeremy Paxman."
He added: "I've got a big, big job to do, I've just got to focus on that. The more I go on about the subject you very kindly raise the more people will babble on about it."
But he said the truth was he did not know what he would do next.
"I understand why people are interested. I would like to have a career either as a romantic novelist or a tighthead prop for England. These things are unlikely to happen," he said.
"The honest truth is I don't know, I don't know and I've got to get on with being Mayor of London."
Mr Cameron has confirmed he had held discussions with the mayor on a possible return to Parliament, telling the BBC Radio 4 Today programme: "My message to him is 'you're a brilliant Mayor of London, you've done a great job, you've got a lot more to give to public life, and it would be great to have you back in the House of Commons at some stage, contributing to public life'. But that's up to him, but I'll certainly be giving him a warm welcome."