Steve Norris is preparing an advertising blitz on the key campaign theme of crime.

A member of the Norris campaign told The Times that some of the advertising sites had been switched to Lib Dem strongholds after a poll suggesting that Simon Hughes was trailing in third place on 17 per cent, with Mr Norris on 31 and Ken Livingstone on 40.

He said: "The original planning was to focus absolutely on our core vote. That is how in the end you win. That is still very important to us, particularly in Outer London boroughs. But we are switching some of the poster areas into Lib Dem heartlands."