Developers are being told they will get permission to build houses, flats and schools on some sites only if they fit them with windows that cannot be opened and mechanical ventilation systems that filter toxins from incoming air.

The “hermetic homes” policy is being forced on councils by the Department for Communities and Local Government, which fears the designation of 700 air pollution zones by local authorities is blighting the 1,400 square miles of prime land within their borders.

Under the department’s national planning policy framework, developments in such areas can now go ahead provided buildings have features such as unopenable windows and filtration.”