Opponents of subterranean developments, which they fear could lead to damp and subsidence in some of the capital’s most expensive streets, are facing a second wave of basement extensions.
Early examples of below-ground living areas are now considered outdated by their super rich owners, who have started applying for permission to extend their extensions.
The latest Londoner to take up trend is Swedish-born Johan Eliasch, 51, the billionaire founder of the Head sportswear brand.
Eliasch, a former deputy treasurer of the Conservative Party and advisor to the British Olympic Association, has applied for consent add a second basement storey beneath his Grade II* listed four-storey Georgian townhouse in Mayfair.
The house already has a sub-basement level featuring a gym, kitchen, staff quarters, and vaults.
According to the application, Mr Eliasch, a close friend of Prince Andrew, wants to add a second floor with space for a wine cellar, two separate rooms for the storage of winter and summer clothes, two further storage rooms, and a garage for his collection of bicycles.
Kevin O’Connor, managing director of Cranbrook Basements, drew up the plans.
He said building beneath an existing basement was “perfectly safe” and that fears of flooding and subsidence were based on “misinformation”.
“In 2009 the Royal Borough of Kensington and Chelsea commissioned a report by Arup Associates focussing on hydrology. They said … [basement extensions]… makes absolutely no difference. There was no ambiguity.”
He said a properly constructed basement would actually improve the foundations of a property, making it less prone to subsidence. And, he said, should neighbouring properties experience minor damage – for example cracked plasterwork – repairs would be paid for under party wall agreements.
However Peter Murray, chairman of New London Architecture, who has helped fight a series of applications for basements around his home in Bedford Park, west London, disagrees. He believes basements can cause subsidence, particularly when built beneath terraced properties, by altering the balance between houses. He also pointed out that basements can disrupt the path of underground water sources, which could lead to damp problems in neighbouring properties.
Subterranean development is increasingly turning neighbour against neighbour in central London. Last month residents stopped traffic as they protested against plans to build a double decker basement in Westbourne Park Road, Bayswater.
Kensington and Chelsea is currently consulting on proposals to limit the size and depths of basements – proposals Mr O’Connor has pledged to fight – while Westminster Council is expected to introduce a policy early next year.
However Murray believes the real solution is for property owners to stop enlarging their homes. “I would suggest that if people want a house of this scale they should move to an area where they can buy one,” he said.