Witanhurst on Highgate's West Hill is London's second-largest private house, dwarfed only by Buckingham Palace.
The original house was built in 1774 but was enlarged to its current 40,000 sq ft in 1913 by Sir Arthur Crosfield, a soap magnate from Warrington, who commissioned architect George Hubbard to design a house which would impress the cream of British society.
Since the deaths of the Crosfields, Witanhurst has been largely empty, other than stints as the base for BBC reality show Fame Academy, and the setting for costume dramas such as Tipping The Velvet, Dorian Gray, Nicholas Nickleby and The Lost Prince.
Witanhurst is now being turned into a modern-day Xanadu, however despite being the size of ten generously sized detached homes, nobody knows who owns it. Indeed, it is said that even Robert Adam, the celebrated architect behind this extraordinary project, does not know who his client is.
The glittering 65-room palace will include 25 bedrooms and 12 bathrooms and an imperial walnut-panelled Grand Ballroom. A vast two-storey subterranean extension will almost double its size, making the property just 2,000 sq ft smaller than Buckingham Palace.
It will feature a 70ft swimming pool, sauna, hairdressing salon, massage parlour and a huge cinema suite. Staff accommodation and parking for 25 cars with a lift to take the vehicles up two flights to street level will complete the £50million expansion.
