The application to redevelop the Grahame Park estate in Colindale included plans to demolish 692 homes currently available at social rent and replace them with just 435.
Having considered the evidence available to him, the mayor withheld his support for the scheme and told Barnet Council, which approved the application in November, they must continue working with City Hall planners and the developer to redesign the scheme to replace the lost affordable homes.
Khan said: “This is a classic example of how not to do estate regeneration. I fully support improving social housing on this estate and across the capital, but this scheme falls far short of what I expect of London boroughs.
“As I have made clear in my new London Plan, estate regeneration projects must replace homes which are based on social rent levels on a like-for-like basis. Londoners so urgently need more high-quality housing, not less, which makes this scheme completely unacceptable in its current form.
“I have asked Barnet Council to work constructively with the applicant on alternative plans with greater density, which do not result in the net loss of affordable homes. Given its recent record in this area, I hope the council recognises the need to replace what would be lost at Grahame Park.”
A Barnet Council spokesperson said: “We are clearly disappointed by this decision. We will now be reviewing this with our development partner to agree the next steps.”