Less than one in five homes built in London over the next 12 months will be classed as affordable, new research by construction consultants McBains suggested.
The survey of housebuilders showed that they were struggling to build enough social and affordable housing to meet demand.
Earlier this month Prime Minister Theresa May warned that she was planning to get tough on developers who did not build houses fast enough.
Sajid Javid, secretary for housing, communities and local government, said that councils which fail to meet their building targets could be stripped of their planning powers.
The chief executive of McBains Michael Thirkettle called for a streamlining of the planning system to help speed up housebuilding.
“Developers are frequently accused of stifling the construction of new homes by ‘landbanking’ - sitting on land so that site values increase. But often the reason is that obtaining planning permission can stretch on for months, if not years, while the developer has already invested heavily in the project. Streamlining the planning system to help developments get off the ground quicker is required,” he said.
The survey showed that housebuilders expect just 16 per cent of the properties they build over the next year to be social housing and just 20 percent to be affordable homes.
According to figures published last month by the Office of National Statistics, the average house price in England is £245,000, but climbs to £482,000 in London.
Thirkettle said: “The chronic need for affordable homes, in London especially, is not being met with less than one in five homes classed as affordable. It means those most in need of housing will find it harder than ever to find accommodation within their budget.”