This week Boris said it would be "wonderful" to be prime minister one day. He said: "It is at least five years away which is an aeon in British politics, by which time whatever my personal ambitions may be there will be thrusting young men and women who will be overtaking me and who knows, it will all be different. In the dim, distant future, obviously it would be a wonderful thing to be thought to be in a position to be considered for such an honour but I think it highly unlikely."

On announcing his campaign to retain the seat of Uxbridge and South Ruislip for the Conservatives, Boris sought to play down suggestions it marked the latest stage of a mission to succeed David Cameron as Tory leader. He said: "No, this is the first stage in the campaign to retain the seat of Uxbridge and South Ruislip for the Conservatives. This is Act One, Scene One of a very long process. There's a lot of digging in to be done."

As speculation began to build when Boris announced he planned to run for parliament, he was forced to refute claims he was building up to a bid for the Conservative leadership. He said "I think it's highly unlikely that that will happen because there's no vacancy. I think David Cameron has been a brilliant prime minister. When David Cameron finally steps down, in 2030, or whenever, it may be that there's a vacancy, but it will probably be filled by a person who's a teenager now."

Boris encouraged speculation about his plans for the Tory leadership when - hours after David Cameron said he would support him in returning to the House of Commons as an MP - Boris referred to Alain Juppé, the former French prime minister and said: “He told me that he was now the mayor of Bordeaux – I think he may have been mayor of Bordeaux when he was Prime Minister. It’s the kind of thing they do in France.”

Asked in an interview for a BBC documentary if he would like to be prime minister one day, Boris said: "Well I would like to be the lead singer of an international rock group. That was my aim. Or a guitarist. I would love to have been a world famous painter or a composer. There are many many things I have done or would like to have been able to do. Obviously, if the ball came loose from the back of a scrum - which it won't - it would be a great, great thing to have a crack at. But it's not going to happen."

Speaking to schoolchildren at south London’s Norwood School, Boris said: "If, like the Roman leader Cincinnatus, I were to be called from my plough to serve in that office, I wouldn't, of course, say no."He went on to repeat his familiar denial, saying that the chances of his actually becoming prime minister were "about as good as my being reincarnated as an olive".However, he added: "If people genuinely wanted me, of course I would want to do it."

While being quizzed by crowds at the Hay Festival back in 2012, Boris said: “As I never tire of saying, my chances of becoming prime minister are only slightly better than being decapitated by a frisbee, blinded by a champagne cork, locked in a fridge or being reincarnated as an olive.”

"Were I to be pulled like Cincinnatus from my plough, then obviously it would be an absolute privilege to serve."

Speaking about the Conservative leadership contest in a conference diary he wrote for The Independent back in 2005, he said: "I'm backing David Cameron's campaign out of pure, cynical self-interest."

When asked by a reader in The Independent to admit that he wanted to become prime minister, Boris said: "My chances of being PM are about as good as the chances of finding Elvis on Mars, or my being reincarnated as an olive."