South London-based Lawray architects has confirmed it is designing a private sports hall for Foxtons estate agents tycoon Jon Hunt, some 15m below the house in Kensington Palace Gardens - dubbed Billionaires' Row.
Kensington and Chelsea planners have approved the ambitious scheme, according to Lawray director Martin Fox, who said the only option for properties in Kensington Palace Gardens is to develop underground.
'It preserves the character of the property and the area,' he told the Telegraph.
Mr Hunt plans to display his collection of Ferraris in the new car museum, according to reports.
Hunt bought the eight-bedroom Kensington Palace Gardens pile in 2005 on a 125-year lease from the Crown Estate for £14 million.