More than 150,000 homes could be built on the green belt under Labour plans
Sir Keir pointed out that in Maidstone, Kent, houses were built on a playing field rather than a car park because the car park was technically in the green belt and was therefore a protected area.
Rishi Sunak has vowed to protect the green belt, sticking to a promise he made during the Tory leadership contest last year.
Oliver Frank, head of residential development research at Knight Frank, called for parts of the green belt to be reclassified to allow for more homes to be built.
He said: “Everybody has a perception that the green belt is completely green and sacrosanct to build on, but there’s lengths of concrete areas and the like that you could actually repurpose.
“If you had that sensible conversation about where you should be building on the green belt, these are the sort of places you should be looking to build on.”
Mr Frank said some local authority areas with parts of the green belt running through them have not met their housing needs because “it’s so easy to block development”.
The green belt was originally designed to prevent urban sprawl – to stop cities like London or Manchester from expanding into the suburbs.
Many green spaces are outside the green belt, such as some national parks and sites of scientific interest.
Steve Turner, executive director of the Home Builders Federation, a trade body, said he would welcome a “sensible debate” about the “societal benefits” of building homes on parts of the green belt.
He said: “The green belt is a planning designation that does not necessarily reflect the ecological value of the land and swathes of it consist of derelict sites. It is larger today than it was 25 years ago.
“Councils have a responsibility to ensure enough land is available to build the number of homes the people in their area need and potential sites should be assessed on how they best match their communities’ needs.”