Kate Barker’s proposal for a planning tax will have a drastic effect on the provision of affordable housing, the Chartered Institute of Housing has warned.

The CIH told the ODPM ministerial taskforce on planning that the idea, part of the economist’s report on housing supply for the Treasury, would “seriously reduce the amount of affordable housing provided through planning obligations”. It did not say by how much.

About 12,000 affordable homes are delivered each year by planning gain deals, where a developer provides social housing in return for planning permission.

Barker’s report recommended that planning gain cover only infrastructure. Other contributions would be replaced by a tax administered by central government.

The CIH said there is no method to ensure this tax revenue will be ploughed back into affordable homes.

Kate Barker has admitted to a House of Commons audit committee that her recommendation for 290,000 homes to be built in the UK each year failed to take sufficient consideration of environmental impact.