Thousands of homes must be built on London’s green belt in order to fix the capital’s housing crisis, Sir Sadiq Khan will argue in a controversial speech on Friday. In a move billed by the mayor as a “radical step-change” at City Hall, Sir Sadiq will say he wants to be “honest with Londoners” that only building on already-developed brownfield land “will never be enough to meet the scale of the challenge”. The mayor’s promise to “forge a new consensus on planning that’s fit for 21st century London” was welcomed by Deputy Prime Minister and Housing Secretary Angela Rayner, who said Sir Sadiq had the Government’s “backing to deliver the housing this city needs”. But the mayor’s political opponents, along with the Campaign to Protect Rural England, believe his new approach will deliver “a devastating blow to the environment and our green spaces”.