After taking office last week, Mayor Khan asked officials to produce an audit of City Hall's preparedness to tackle the housing crisis.
The report showed a "shocking scale" of 'affordable' housing delivery, with the previous mayor delivering the lowest number of new 'affordable' homes since records began in 1991 (4,880).
In addition, only 13% of the homes were progressed through planning permissions granted under Mr Johnson's term.
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With the report also highlighting a growing construction skills crisis and a "flawed process" of identifying public land for homes, Mayor Khan has accused Mr Johnston of "grossly letting down Londoners".
"London gave me the opportunity to go from the council estate where I grew up to being able to buy a family home we could afford. But today, too many Londoners are being priced out of our city," he said.
"One of the first things we did when we got to City Hall was open the books and look at what was already in the pipeline and it seems the previous mayor has grossly let down Londoners by leaving the cupboard bare when it comes to delivering affordable housing.
"I am determined to fix London's housing crisis and ensure that all Londoners have the opportunity to rent or buy a decent home at a price they can afford, but the scale of the challenge is now clearer than ever and we're not going to be able to turn things around overnight.
"We will be outlining our plans in the coming months, but one of the first things we can do is work with Transport for London to fast-track their numerous surplus sites for development that have previously just been sat on."
(LM)
