Two landlords must pay a combined total of over £300,000 following legal action by a central London council.
Westminster council claimed that in both cases extra rooms were illegally squeezed into properties and then let out, without the appropriate planning permission.
The authority used the Proceeds of Crime Act in both cases to recoup more than the maximum £20,000 fine.
The council can keep up to 37 per cent, with £86,393 being recouped for Westminster tax payers.
A council spokesman said: “This is a clear warning to anyone who thinks they can ignore planning laws and benefit financially. Cramming people into tiny properties and disregarding the need for planning permission is dangerous and puts tenants at risk.”
Yesterday Letting Agent Today reported on the use of the Proceeds of Crime Act to leave one landlord in north London with a bill of over £700,000 after he breached planning enforcement notices.