Boris Johnson says he backs David Cameron 'all the way'
Boris Johnson has denied that he wants to see David Cameron "fail miserably".
The London mayor said he was "backing David Cameron all the way" and was "increasingly confident" the Tory leader would win the next election.
Ex-No 10 press chief Andy Coulson said in an article for GQ Mr Johnson was ready to ride to the rescue if Mr Cameron failed to win the election.
"Grateful as I always am to Andy for career advice, I am backing David Cameron all the way," the mayor said.
"I'm backing David who I am absolutely increasingly confident is going to win," he added.
In his article Mr Coulson recalled that the PM had joked about Mr Johnson's ambition to be Conservative leader.
But he said he thought Mr Johnson would rather David Cameron "failed miserably" at the next election rather than "stab him in the back" with a leadership challenge while he was still prime minister.
He said: "Stabbing David, or anyone else for that matter, in the back would be distinctly off brand, just not very Boris."
Mr Johnson's second term as London mayor ends in 2016.
In a recent interview with Michael Cockerell for a BBC documentary, Mr Johnson was asked if he wanted to become prime minister. He answered: "If the ball came loose from the back of the scrum, which it won't of course, it would be a great, great thing to have a crack at."
In his article Mr Coulson said that "when Boris asked me to pass on the message that he was keen to stand as mayor of London (in 2007), David [Cameron] responded, 'Well, if he wins, he'll want my job next'.
"If proof were needed that our PM is a man untroubled by self-doubt, it came in his next sentence: 'So I think he'll be a bloody brilliant candidate for us'."
Mr Coulson resigned from Downing Street after becoming embroiled in the phone hacking scandal.
He faces charges relating to phone hacking and alleged conspiracy to bribe public officials for information, alleged offences that date back to his time as editor of the News of the World.