Boris Johnson declined to rule out the possibility of a future bid to become Conservative leader and Prime Minister, but insisted he supports David Cameron and said rumours about his ambitions were "a distraction" from his job as Mayor of London.
Challenged to say that Mr Cameron was a better man than him to be PM, Mr Johnson would say only that it was "unverifiable". He said that "for the next few years" he only wanted to be mayor, but added that "heaven knows" what he will do after his four-year term ends in 2016.
Speculation that Mr Johnson has his eye on Mr Cameron's job is dominating the Conservative Party conference in Birmingham, after a poll suggested voters prefer the London mayor to Mr Cameron by a wide margin.
The survey by pollsters Opinium for The Observer gave Mr Johnson a net +30 rating compared to -21 for the Prime Minister.