Fifty feet below street level, under the garden of an eight-bedroom mansion, what might be London’s most lavish basement is under construction. The equivalent of four storeys, it will house a showroom for a multi-million pound vintage Ferrari collection and a sports hall big enough to fit a tennis court, a swimming pool and a gymnasium.

Jon Hunt, founder of the Foxtons estate agency, is building this underground extravaganza because his home, a trophy property located in Kensington Palace Gardens and protected with Grade II status by UK heritage laws, cannot be expanded in any other way.