Boris Johnson was given a thunderous reception by activists at Tory conference tonight - but insisted he was completely loyal to David Cameron.
The London Mayor received a standing ovation after he delivered a gag-laden speech to more than 1,000 members at a fringe event.
He was heralded on to the stage in Birmingham with a video describing his re-election in the capital this year as "Mission Imborisable".
But while he boasted of achievements such as cutting crime in London, Mr Johnson played down speculation that he wants to take the Prime Minister's job.
"It is sometimes inevitable that the mayor of a great city will find himself saying things that do seem at variance with national policies," he said.
"Of course I am going to continue to lobby for a long term solution to our aviation capacity problem.
"No-one as a result should have any cause to doubt my admiration for David Cameron."
He stressed he was one of the first "Cameroons" in the 2005 Tory leadership contest.
"I believe that in tough circumstances he, George Osborne, are doing exactly what is needed for this country and to clear up the mess that Labour left.
The ConservativeHome.com event was given the tagline "Re-elected and Olympotastic".
Mr Johnson used an article in the Daily Telegraph this morning to warn that government was not addressing the plight of the "struggling middle" - working families with incomes ranging from £30,000 to £64,000.
Yesterday he declined an opportunity in a radio interview to say that Mr Cameron was a better Prime Minister than he would be, insisting the question was "unverifiable".
The mayor is due to give a keynote speech from the platform of the conference itself tomorrow, which will be scrutinised for evidence of his intentions.
Polls have suggested the Tories would get a significant bounce if he was in charge.
However, the prospect was given short shrift by veteran Cabinet minister Ken Clarke.
Mr Clarke told a meeting hosted by Channel 4 on the fringe of the conference: "If he really wants to be a prime minister for serious reasons and not just getting his picture in the paper more often, he really does have to settle down and demonstrate he can seriously deliver on some complicated subjects."
Mr Clarke later dismissed talk of a leadership challenge as "conference hoo-hah" and urged Mr Johnson to "calm down".
He told a fringe hosted by The Independent: "Boris has been created as a rival because he has had such favourable publicity over the summer. My advice to him is to calm down.
"There isn't a vacancy at the moment. How is he supposed to be vying for the leadership I haven't the least idea.
"My advice to Boris is get back to the day job and demonstrate you can be a serious leader of a local large city government and a serious deliverer of policy."
He added: "There isn't the remotest chance of the leadership becoming vacant. Why should he rule out coming back to Parliament? By 2014 'Boris for leader' will be a dead story - it will probably be a dead story in a fortnight's time.
"God knows when we are going to have another Prime Minister. It certainly isn't going to be in the next 12 months, 24 months or three years."
Mr Johnson was mobbed as soon as he stepped off the train in Birmingham, with passers-by chanting "Boris! Boris!" as he fought his way through ranks of TV cameras and photographers.
And he was greeted by more reporters and cameramen at the Hyatt Hotel.
At one point the mayor was trapped in front of the cameras after getting into a lift whose doors would not close.
Mr Johnson indicated he wants a return to grammar school-style education system, telling Tory members he believed in "some form" of selective education.
"I'm a strong believer in competitive education," he said.
"I personally have no objection to selective admission at some stage in a child's development."
He added: "Thankfully, I suppose, for the party policy I'm not in a position to do this."
Mr Johnson also used the rally to reiterate his opposition to any attempt to build a third runway at Heathrow, telling the crowd the only options were to build in the Thames estuary or find a "long-term solution" at Stansted.
"I suggest to my friends in government and everyone here who thinks that's the answer, move off that idea. It is not going to happen. We need a better solution."
Mr Johnson told the 1,000 strong-crowd that London was the greatest city in the world, recounting a story about a squirrel that "savaged" a member of the boyband One Direction as proof.
The Mayor said he had "every sympathy" with Niall Horan, who underwent knee surgery after being attacked in Battersea Park, but added: "In London, not only do we have such beautiful greenspace, but such healthy, well fed dynamic and musically discerning squirrels."
Mr Johnson also sparked laughter with a risqui joke about plans for a politicians' Olympics team.
"Jeremy Hunt wanging the bell-end, John Prescott with the crocque, Seb Coe in the 100m and of course Ed Miliband for the high jump."
Asked if he was flattered by the media attention, the Mayor said it was "very, very bad for my ego" and a "distraction".
Speaking as he left a private reception, Mr Johnson added: "I think Ken Clarke was on the money earlier on when he said that it was a distraction and it needs to end."
Asked what qualities a leader needed, Mr Johnson, who was being pursued by the press through the conference centre, said: "The ability to get through a huge scrum of journalists."