The Green Party has declared Darren Johnson as its candidate for next May's London mayoral election.

Johnson, an openly-gay member of the Greater London Assembly, will pit himself against Ken Livingstone, Steve Norris and Simon Hughes for the top London job.

He has seen off a challenge from Green candidates Jenny Jones, Tom Walsh and Hugo Charlton - securing 55 per cent of the votes cast.

"I have a clear track record of winning elections and look forward to heading the strongest Green challenge ever in London," said Johnson.

"Ken Livingstone has introduced important initiatives, such as congestion charging and affordable housing targets, which have our support.

"On other issues, however, he has been a disappointment, favouring new road building, airport expansion and a development plan that puts big business before local communities.

"Simon Hughes, Steve Norris and Nicky Gavron will be offering just more of the same.

"For Londoners looking for something fresh, I will be providing a genuine Green voice in this contest and will fight hard for every vote."

He is standing on a radical ticket which involves a £3000 a year parking levy on company car-parking spaces and expanding the congestion charge scheme.

Johnson is also committed to halting Livingstone's plans for new road crossings in East London, declaring a complete end to road building in the capital.He would also make solar panels compulsory in all new developments to combat climate change.