30ft - Deep hole in the back garden.

Mansion whose mega-basement is at the centre of one of Britain's biggest building rows goes on the market for £25m – complete with 30ft-deep hole in the back garden.

On the face of it the Grade II listed Georgian home, on Brompton Square, in Knightsbridge, has just about everything a wealthy buyer looks for in central London.

It has a sought-after address, boasts one of the area's largest private gardens and has the potential to be turned into a nine-storey mansion which is 25 times the size of the average English home.

But the property has attracted anger from neighbours for almost a decade after the garden was turned into an eyesore by its owner.

Achilleas Kallakis began digging a basement to house a swimming pool, spa, cinema and car lift in the mid-2000s.

The project was abandoned when workers downed tools in 2008 and, in 2011, it was sold to its current owner for £28 million.

Plans approved by the Royal Borough of Kensington and Chelsea show the whole of the basement's bottom floor will be the underground garage.

Above that will be the swimming pool and gym. Basement -2 will be a 'family space' along with music room, music store and cinema. Basement -1 will have three guest bedrooms - all with en-suite - along with a kitchen and laundry room.