Controversial former police chief Brian Paddick will enter the battle to become London's mayor this week.
The 49-year-old is reported to be planning to earn the Liberal Democrat's nomination.
The move would see Mr Paddick fighting it out with current Mayor Ken Livingstone and Conservative MP Boris Johnson ahead of next May's election.
Mr Paddick, a former Lambeth borough commander who went to Sutton Manor High School, retired after clashing with Commissioner Ian Blair over the handling of the Jean Charles de Menezes shooting in July, 2005.
Before his retirement Mr Paddick was criticised for his softly-softly approach to cannabis use.
He was also the highest ranking openly gay officer in the Met.
Balham-born Mr Paddick has vowed to improve London's bus network and make sure the Congestion Charge hits high-earners rather than delivery drivers.
The Lib Dems' candidates will be announced in November.
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