Banker digs deep for Holland Park project

But investment bankers do things on a far grander scale. A 30ft chasm has opened up behind a family home in Holland Park which will house a 16metre swimming pool, a mini-spa with a Jacuzzi and treatment room, a huge kitchen and a car park with room for six vehicles.

It is one of the more spectacular examples of the rash of domestic excavations in the "City bonus belt" of Kensington, Notting Hill and Knightsbridge.

The garden will be restored on top of the subterranean extension, leaving few signs of the massive project, due to be completed by the end of next year.

The work has been commissioned by Omar Bayoumi and his wife Norma Bastos, a property developer. Mr Bayoumi, 52, is joint head of mergers and acquisitions at Mayfair investment bank Fairfax. He was formerly head of capital markets at German Commerzbank.

The couple bought the house for £12 million in December 2005 and are likely to be spending at least £2 million more on the building work.

The house served as a hostel for the blind in the Fifties and Sixties and was the Burmese Embassy in the Seventies before becoming a family home again in 1978.

The couple also own a riverside property in Sonning, Berkshire, and a home in Notting Hill. Last year they sold a large Victorian house in Pembridge Place for £7.5 million after being granted planning permission for a similar programme of work.

Stuart Robertson, principal architect at 23 Architecture, said the car park, which will be reached from a side road, was an unusual feature.

He said: "This design gives you the opportunity to park your car privately and access your house or go straight to the swimming pool."

Mr Robertson added: "Subterranean extensions are quite a costly thing to do but with all the restrictions and the nature of London there are not many opportunities to extend above ground.

"The only place you can get a really substantial extension is underground."

One of most spectacular planned excavations is at the Kensington Palace Gardens home of Foxtons founder Jon Hunt. He wants to excavate 50 feet to create a sports hall with a tennis court, pool, gym and viewing gallery and a motor "museum" for his collection of vintage Ferraris.

Ricky Gervais is digging out a huge basement at his home in Hampstead which will have a pool, games room and golf simulator.