Mayfair residents fear their neighbour building an illegal basement in a £9million townhouse near a row of 18th Century properties could have compromised the homes’ structural integrity.
Neighbours suggested the historic properties are already structurally frail due to when and how they were built.
They fear the unauthorised "iceberg" basement underneath 74 Park Street, which included a gym and sauna, could cause homes to sink further into the ground, a problem residents say is common in this part of town.
The building's owner Stefano Menconi has been ordered to fill the basement in with concrete by next year.
Stewart, a seasoned concierge filling in at 71 Park Street, told the Local Democracy Reporting Service (LDRS), many of the properties along Park Street were built in the late 1700s.
He said: "The basements around here are already sinking. The properties are old and have their own structural faults. Who knows what the impact of building an underground basement will be?"
One neighbour, who did not want to be named, said Park Street in recent years has experienced a wave of the super rich buying properties and redoing them. She said it wasn't uncommon for someone to purchase a recently renovated property only to redo it themselves.
She said: "We are sort of used to that. After all, this area attracts wealthy people more and more but the homeowner's actions are not something someone would like. People who want to build in this country need planning permission. Planning restrictions may be annoying but they are in place for a reason."
Italian businessman Mr Menconu had purchased the property for just short of £3 million in 2010. It is now estimated to be worth £9 million by property experts.
According to the middle-aged homeowner, who has lived in the neighbourhood for 23 years, it's this wave of the uber rich which has permanently transformed Mayfair. She suggested local businesses are being pushed out by high-end retailers trying to snap up some of the luxuriously rich's cash.
She said in recent years, the local butcher, the photographer's and the "beloved" local Pain Quotidien, a cafe chain, have disappeared and been replaced with expensive clothes shops.
She said: "Over the years the area has changed a lot. There used to be an eclectic mix of neighbours but now it's full of the super rich. It's making the area more isolated. You don't know who your neighbours are."
Another neighbour, who also did not want to be identified, said the unauthorised refurb was "simply not right". He said: "It's not fair for the neighbours. What if it comes to damage your neighbours' properties or your own in 10, 20 maybe 30 years' time?"
The Planning Inspectorate has ordered Stefano Menconi, the owner of 74 Park Street, to restore the Grade II-listed building after an unsuccessful appeal. This means filling in the basement, where he installed a cinema, gym and sauna, with concrete by this time next year.
Electrics and plumbing will also need rerouting while fixtures and fittings must be restored to their original status. Westminster City Council said the alterations, which included changing ceiling heights, were refused planning permission in 2010.
Inspectors said the changes would harm the building's "special architectural and historic interest". But Mr Menconi pressed ahead and in 2023 the council served him with a notice requiring him to remove the unauthorised works.
He appealed to the Planning Inspectorate, which sided with the council. Mr Menconi was ordered to pay for some of the council's costs.
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.
He 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."
Mr Menconi has been contacted for comment.
