The Liberal Democrat mayoral candidate, Brian Paddick, has told BBC London he will cut crime and improve transport.
Brian Paddick has promised to cut crime or stand down
He said British Crime Survey statistics showed crime had not fallen in London, despite Wednesday's figures from the Metropolitan Police (Met).
Mr Paddick has promised to cut crime in London by 20% during his first term if he is elected.
He also told BBC London he would improve public transport, with a plan to shorten bus routes to curb delays.
Mr Paddick said the Met's figures were not as accurate as the British Crime Survey's statistics. The survey questions 3,500 Londoners to try to draw an accurate picture of crime in the capital.
The former policeman said: "During the run-up to the last election Ken said he would cut crime by 50%. Whichever measure you take, the police's or the British Crime Survey, Ken hasn't cut crime anything like 50%."
On transport, Mr Paddick said he objected to the extension of the Freedom pass for over-60s to include rush hour travel, saying it would add to congestion for commuters.
He proposed shortening bus routes so buses were less affected by delays, and use GPS tracking to stagger buses.
Mr Paddick won 73% of the first preference votes during the Lib Dem contest.
'Stop the slaughter'
This year two teenagers have been stabbed to death in London while 26 teenagers 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 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 current mayor Ken Livingstone, the Labour Party candidate, and the Tory candidate Boris Johnson.