Hundreds of people have gathered outside City Hall to campaign for more affordable homes in London.
London Citizens, an alliance of civic groups, said not enough help was being offered to average-income Londoners.
It said Community Land Trusts (CLT) could be the solution, where land was provided for free, so buyers paid less for their homes.
London Mayor Ken Livingstone, who is backing their campaign, has announced plans for a CLT scheme in east London.
London Citizens' Our Homes, Our London campaign is calling for the creation of more CLTs.
CLTs have been used in the US for years, enabling low-paid people to get on the housing ladder.
In the UK, the government's housing green paper "Homes for the future: More affordable, more sustainable", supports the piloting of 14 CLTs across the country.
Campaigners gathered outside City Hall on Monday to call for local authorities and other landowners to release land for future CLTs.
Simon Okotie, a member of London Citizens from the London Buddhist Centre, said: "Everyone who has looked at the CLTs knows they are the obvious solution to London's property apartheid and the scandal of overcrowding.
"What we're asking for now is local authorities and other landowners to get on board by releasing land to London's communities."
Mr Livingstone is working with Tower Hamlets Council in east London to create a CLT in Bow Water, which hopes to create 300 affordable homes ready for occupancy by 2011.
"I believe that Community Land Trusts can complement our other initiatives," he said.
"We will work hard with Tower Hamlets Council and the community towards making this first pilot a success."