The research shows that since 2013, almost 16,000 houses have been built under PD rules in London.

The report, Slums of the Future – Permitted Development Conversions in London, claimed that over half of these homes didn’t meet minimum space standards.

Mr Copley’s report urges Sadiq Khan to add to the pressure on the Government to scrap PD and believed that “subjecting London families to cramped, substandard and unaffordable homes” was not the way to solve the national housing crisis.

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“Permitted development is an unnecessary and deeply flawed policy. 

“If this continues unchecked, we will be condemning tens of thousands more Londoners to living in miserable conditions.

“Some may call them ‘rabbit hutches’ or others ‘micro-homes’, but we must be clear about what we are building when we allow masses of permitted development conversions: the slums of the future.

“We’re already seeing vast swathes of office space wiped out at an unnerving rate.

“They should be condemning this policy to the scrap heap.”

The government confirmed on 25th May that it would extend the rules for permitted development to include home extensions and allow shops to convert to office space without the need for a full planning application.