Boris: I'll limit time as Mayor to two terms

The Tory candidate promised that, if elected, he would bring forward legislation to limit the amount of time he could serve to eight years.

Ken Livingstone has said he would like to go for a fourth term, despite originally ruling out standing beyond his second, which would mean him running London in his seventies.

Mr Johnson said: "It is incredible that he's serving more than two terms. I certainly won't. One of the things we should do is bring forward legislation to stop any Mayor for more than two terms because, there's no doubt about it, the whole thing has become seamy and out of control."

He denied bringing in a term-limit would result in the Mayor becoming a lame duck incapable of making significant changes during his last two years in power.

"Nonsense, you still have fantastic potential to do things, get things done according to your agenda," he told LBC radio.

"You are released from the fear of having to suck up to the media, from the fear of re-election."

Mr Johnson will announce this week plans to "clean up" City Hall after a string of serious allegations about the financial probity and accountability of Mr Livingstone's team.

"It's time we had a new regime and cleaned up all that mess. I don't think it's right that the Mayoral advisers should go so completely unscrutinised," he said.