The owner of an 18th century townhouse in Mayfair has been ordered to destroy an unauthorised basement that includes a gym, sauna and cinema.
The Planning Inspectorate has ordered the homeowner to “restore” the Grade II-listed building in Central London after an unsuccessful appeal.
This will mean pouring the 860 sq ft “iceberg” basement with concrete by this time next year.
Meanwhile, electrics and plumbing will have to be rerouted, while fixtures and fittings must be restored to their original status.
The cost of the works, which were given a 12-month deadline for completion, will likely run into hundreds of thousands of pounds.
Westminster City Council said the alterations, which involved altering ceiling heights, were denied planning permission in 2010.
The decision came shortly after an Italian entrepreneur had purchased the property for nearly £3 million through a company registered in the United States.
Inspectors deemed the changes would harm the four-storey building's "special architectural and historic interest".
But the owner of the home — estimated to be worth around £5 million — decided to go ahead with the refurbishment, despite being told not to.
In 2020, the local authority discovered that the owner had ignored the ruling and had excavated the existing basement.
The council also discovered that historic features of the house, such as panelling and fireplaces, had been removed.
It served a listed building enforcement notice in 2023 requiring the removal of “the unacceptable unauthorised works”.
Those who ignore planning rules will be held accountable
The owner appealed the notice, but the Planning Inspectorate sided with the council, ruling the works and extension unlawful.
The government body also made a partial award of costs to the council for the costs incurred.
Geoff Barraclough, the council’s cabinet member for planning and economic development, said the owner showed a "complete disregard" for the historical significance of the property.
The Labour councillor added: "I hope this outcome sends a clear message: those who ignore planning rules will be held accountable.
"It is simply not acceptable to carry out works that have been explicitly refused listed building consent."
“We remain committed to safeguarding Westminster's unique architectural heritage."
