The London Assembly has demanded funds to build a tram network to cross the Thames linking Waterloo with Euston, with branches to Camden Town and King's Cross in the north, and Brixton and Peckham in the south.
Research and design of the tram scheme is funded until 2010, but the tram's future is not yet assured as there is no funding.
The London Assembly voted for a motion to build the tram, and has called on the Mayor, as Chair of Transport for London (TfL), to fully explore all possible options to secure the funding to get it up and running.
Val Shawcross AM, who proposed the motion, said: "There is clearly a very real need to progress the Cross River Tram to combat the woeful inadequacies in public transport services, particularly in some parts of south-east London, and alleviate overcrowding on the Tube.
"I'm sure anyone who has tried, and failed, to board a Northern Line train during rush hour would agree with me. If the Mayor is committed to reducing the environmental impact of road transport, he has to find ways of implementing more eco-friendly modes of public transport like the Cross River Tram, to encourage people out of their cars," she said.
Caroline Pidgeon AM, who seconded the motion, said: "I appreciate that TfL is under pressure to deliver a number of major transport projects, but the associated regeneration benefits, and the desperate need to improve north-south transport links make this scheme absolutely vital.
"I urge the Mayor and TfL to really think creatively about the funding – including phasing delivery of the project - to assure the future of the Cross River Tram as we simply cannot let this scheme be lost. We certainly cannot afford the huge costs to London of the scheme not going ahead."
The motion reads:
"This Assembly supports the development of the Cross River Tram scheme and the extension of the existing Croydon Tramlink network, and believes that the development of London's public transport system is vital for the continuing regeneration of London and the relief of peak period overcrowding on London's underground and overground train networks. This Assembly calls upon the Mayor as Chair of TfL to ensure that all possible options for the funding of these schemes are fully explored."
The motion was deadlicked 11:11, with: 10 Conservative and 1 BNP member voting against the motion, and 7 Labour, 2 Liberal Democrat, 2 Green Party Members voting for.
The Labout chair's casting vote carried the motion.