Brian Paddick today launched a stinging attack on Ken Livingstone and said the Labour Party should be "ashamed" to have him as a candidate.
Mr Paddick, a former Met Commander, will tomorrow use his speech at the London Lib-Dem spring conference in Canary Wharf to hit out at his Labour rival.
It comes after Mr Livingstone was accused of anti-semitism by members of the Jewish community.
The Labour candidate has since written a letter of apology for the language he used during a meeting with Jewish leaders.
In his speech tomorrow Mr Paddick will liken Mr Livingstone to a "bad seventies comedian".
He will say: "Like a bad seventies comedian, he plays to the gallery and doesn't care who he upsets in the process.
"He should be ashamed of himself. And Labour should be ashamed to have him as a candidate.
"He doesn't care if he divides Londoners. Well I do care, and as Mayor, I want to unite Londoners."
A spokesman for Mr Livingstone today declined to comment.
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