The London mayor’s target of making 50% of homes on each development affordable could be preventing 8 million ft2 of empty office space from being developed into 12,000 new homes.

A report published by the Greater London Authority’s land assembly and development taskforce last November recommended that 8 million ft2 of empty office space in London should be turned into homes.

But three months after the report was published, the buildings, mainly in the west of the city, are still empty. The project has met resistance from developers that do not want to lose money by turning half of their office space into social housing.

Terry Fuller, chair of the affordable housing group at the House Builders Federation and adviser on the taskforce, said that without full corporation grant “these spaces will remain unused”.

Steve Douglas, the London director of the Housing Corporation, who was also on the taskforce, said: “Some of the key recommendations [the taskforce] made will end up in the London housing strategy. It is a work in progress.”