‘Four million’ homes could be built on green belt in Angela Rayner’s planning revolution

This includes releasing grey belt land – which Labour previously suggested would be made up of “disused car parks, dreary wasteland” – for development in the green belt.

But her proposed changes to the National Planning Policy Framework (NPPF) may go far further in unlocking green belt development than anyone had expected.

Based on an assumption that grey belt land would be limited to so-called brownfield sites where there had been past development, LandTech had previously identified space for 316,000 green belt homes.

But Harry Quartermain, LandTech’s head of research, said the actual figure could in fact be more than 10 times this based on the actual definition of grey belt land published by Labour in the draft NPPF, which is under consultation.

Mr Quartermain said Labour’s new definition of grey belt land could unlock 150,000 hectares of land for development, roughly 10pc of the total green belt, with scope to build between 2.5m and 4m homes.

Mr Quartermain said: “It’s radical because they have made it clear that there are circumstances in which development on the green belt is no longer inappropriate.”

The draft NPPF states that grey belt land will be not only previously developed land but also land that makes “a limited contribution to the five green belt purposes”, which are primarily to stop urban sprawl.

The draft NPPF also states that building on the green belt should not be considered inappropriate if it can be done sustainably on grey belt land.