Brian Paddick has promised to cut crime or stand down

Launching his campaign in Brixton, south London, Mr Paddick said if he fails to achieve his crime reduction target he will stand down.

He also promised to "increase reliability" of buses and the Tube and increase affordable housing.

He won 73% of the first preference votes during the Lib Dem contest.

'Stop the slaughter'

This year two teenagers were stabbed to death in London while 26 teenager's were killed on the city's streets last year.

Mr Paddick said: "I have a track record of performance against Londoners' number one concern; crime... It's time for someone who can stop the slaughter on our streets.

"I will cut crime in London by 5% every year over the course of my first term in City Hall.

"And I will take personal control of ensuring this target is met by chairing the Metropolitan Police Authority. If I fail to reach my target after four years, I will not stand again."

As the Metropolitan Police Borough Commander for Lambeth in 2000, Mr Paddick's approach to cannabis - which saw officers cautioning rather than arresting people caught with the drug - brought him to prominence.

Mr Paddick, who resigned from the Metropolitan Police in May 2007, will be competing with the incumbent mayor Ken Livingstone, the Labour Party candidate, and the Tory candidate Boris Johnson.

The Green Party has put forward environmental campaigner Sian Berry for the post while the British National Party's candidate is Richard Barnbrook.

Lindsey German is standing for the Respect Party and former boxing champion Winston McKenzie is contesting as an independent.