‘Prat’ Boris rules out prospect of Number 10

London mayor Mr Johnson was repeatedly asked in a television interview if he would like to be the next Prime Minister but dismissed speculation as a “silly season” story.

The mayor was shown footage of him stuck last week on a 150ft high, 1,000ft long zip wire in an east London park, when he was left hanging over a crowd of people for several minutes as the wire lost momentum.

“There you have got it, how on earth could you elect that guy? How could anybody elect a prat who gets stuck in a zip wire?” Mr Johnson joked.

“I tell you what happened, I was trying to publicise our live site in Victoria Park, which is a wonderful place, by the way.”

He added that the experience had been “slightly scarier” than it appeared, joking that his actions had been “heroic.”

“After I got stuck on that thing, we did have a big increase in the number of visitors, so it wasn’t totally fatuous, contrary to appearances,” he said.

Asked if he fancied being Prime Minister, he responded: “No, of course not, because I have got four years of mayor of London ahead ... perhaps this is the moment to knock this once and for all on the head?”

He added that one of the most moving aspects of the Olympics had been the number of volunteers.

He said: “They are doing stuff in their own free time.

“Wouldn’t it be a wonderful thing if we could mobilise them, and people who want to join them, through Team London to help with sport in schools?

“It is often not the shortage of facilities, the problem is a shortage of people who have got the CRB checks and all that stuff who are willing to come and help out.”

Asked whether Mr Johnson would make a good Prime Minister, David Cameron said: “He’s got his term to serve as Mayor of London.”