The Abu Dhabi-owned developer won planning approval for the 268-home mixed-use redevelopment of the Metropolitan Police’s HQ site in April 2016.

Then Mayor Boris Johnson waved through the Westminster scheme with an offer of a £10m payment and only 10 affordable homes.

Since then developer BL Developments has sought to increase the total number of homes by 27, from 268 to 295, with no increase in the number of affordable units or payment in lieu, meaning the level of affordable housing fell further still to only 3%.

Developer BL Development, which is owned by the Abu Dhabi Financial Group, plans to build six residential-led buildings ranging from 14 to 20 storeys on the 1.78-acre triangular site just south of St James’s Park in Westminster.

The Abu Dhabi Financial Group bought the building for £370m in December 2014, and then appointed Northacre, in which it is a major shareholder, as development manager.

Sadiq Khan said: “This is a site which has only recently been transferred from public ownership and sits within one of the most expensive areas of the country.

“Having carefully considered the evidence available to me, I have decided to refuse permission for this amended application.”

He added: “A shortage of affordable homes is at the heart of the housing crisis in our city.

“The scheme put forward for this site is simply unacceptable: it fails to provide the maximum amount of affordable housing that could be delivered on this landmark site, and follows a previous application in which the affordable housing provision agreed by the previous Mayor was already appallingly low.

“It beggars belief that the initial application was approved under the previous Mayor with a paltry 4% affordable housing, just days before the Mayoral election.”

The decision comes just a few weeks after he slammed Wandsworth Council for allowing Battersea Power Station’s developers to slash the amount of affordable housing by 40%, from 636 homes to just 386 – or only 9% of the 4,239 homes across the scheme.

The Mayor had no formal power to intervene under current planning regulations, but wrote to the Council to object to the decision in the strongest terms.

Khan added: “I am more determined than ever to do all I can to ensure Londoners are not short-changed when it comes to developers doing their bit to help tackle London’s housing crisis.

“The government now needs to show it is committed to this too and devolve the powers to help me stop developers getting away with unacceptably low levels of affordable housing.”