Peers have slammed Sir Keir Starmer’s plans to build homes on already-developed parts of the green belt as “largely redundant”.

The House of Lords Built Environment Committee wrote to Housing Secretary Angela Rayner to warn the policy is “unlikely to make any significant difference” to the number of new homes that can be built.

Lord Moylan, chair of the Committee, said: “The Government’s policy has been implemented in a somewhat rushed and incoherent manner.

“The committee does not believe that it is likely to have any significant or lasting impact on planning decision-making or helping the Government achieve its target of building 1.5 million new homes by the end of this Parliament.

“In December the Government published the final National Planning Policy Framework and the revisions it has made to the framework have now made the concept of grey belt land largely redundant as land will now be more likely to be released from the Green Belt through existing channels instead.

“The Government also does not seem to have any plan to measure progress or determine the success of this policy. Effective policy must be evidence based and be able to demonstrate its efficacy. Sadly, this is not the case here.”

There is “significant uncertainty” about how many homes could actually be built on grey belt land with estimates ranging from as low as 50,000 up to four million.

The Lords added: “This uncertainty is compounded by the fact that the Government does not have a clear plan to track the progress and assess the effectiveness of its new policies.”

The government has previously described the grey belt as “poor quality and ugly areas” on parts of protected land, called the green belt.

Analysts have suggested England could have an estimated £850billion of grey belt.

There could be 30,597 potential grey belt sites totalling 7,6215 hectares, specialist property lender Together suggested.

This would be enough to build 2,362,680 new homes with an estimated development value of £850,272,243,386, an analysis by software firm Searchland said.

The green belt covers about 13% of England and was designed to limit the growth of large built-up areas, and to stop large towns merging into one another.

Under the Labour government’s plans, if a council’s housing targets cannot be met some existing green belt land will be re-designated as grey belt.

This is as part of its plans to build 1.5 million new homes over this parliament.

A spokesman for the Housing department said: “We have inherited the worst housing crisis in living memory and are taking decisive action to deliver 1.5 million homes as part of our Plan for Change, including overhauling the broken planning system.