The three-bedroom penthouse, with 2,265sq ft of living space and rooftop terraces with views and “al fresco dining space for 10”, is on sale for £8.95 million. In the middle, the two-bedroom first-floor apartment, at 1,601sq ft, is £5.95 million.

But the three-bedroom basement apartment is on the market for £13.25 million. It covers 4,451sq ft of the ground and lower-ground floors and includes a screening room and wine cellar, two outdoor terraces and a garage.

You may not get the city views, but light wells, living walls and floor-to-ceiling windows, where the ceilings are up to 10ft high, bring in natural light and a sense of the outdoors.

  Photo: Finchatton

“It is quite simply the most magnificent apartment in the development,” says Alex Michelin, co-founder of Finchatton, the design and development company behind Knights House. “This is the first time we’ve launched an apartment at ground and lower-ground levels which has been the most desirable apartment in the building.”

The drawing room’s proportions, along with the high ceilings and the property’s width are more befitting a £25 million town house than a Knightsbridge apartment, says Michelin, and the property is a showcase for bespoke craftsmanship, from the marble in the master bedroom to the curve of the custom-made staircase.

Light floods in to the open-plan reception room through architectural glass roof lights and a frameless sliding door system that opens on to one of the terraces.

  Photo: Alamy

Due to London’s restrictive planning laws it is becoming more difficult to add space or floors to the tops of buildings, so making the most of the basement is the solution for many developers and home owners wanting to expand.

“Londoners have no real option but to create good basement spaces. We feel good design can overcome all the traditional downsides of lower ground floor living and can provide immense potential to add value to a scheme that might otherwise be an unattractive development proposition,” says Michelin, who has recently completed a basement home in Eaton Square, in Belgravia, that offers another benefit of these type of flats: sole access to the rear garden.

“Some buyers also prefer a private entrance, which many basement apartments offer. In summer, these units are also typically cooler than units above ground,” he says.

A further benefit, says Simon Deen, at Aston Chase, is that ground and lower-ground floor flats lose no space on the lower floor to communal areas. He is selling a basement with five bedrooms, high ceilings and a private 120ft garden in Hamilton Terrace, St John’s Wood, for £5.25 million.

Like Knights House, St James House, a Grade II listed building overlooking the gates to St James’s Palace, places its biggest, showpiece residence on the bottom.

  Photo: Alamy

The eight apartments, which Strutt Parker is due to start marketing next spring with prices from around £20 million, include the 10,300sq ft triplex residence on the first, ground and two lower-ground floors, with four bedrooms and higher ceilings than any other property in the building.

While period redevelopments can go to town with the ornate features, new developments optimise subterranean space for very modern lifestyle luxuries.

In the 1826 – the former Bromley Arms pub in Fitzrovia, now turned into four apartments – the ground-floor duplex flat comes with a cinema room and vaulted indoor spa.

“One of the first things people say in their property search is ‘no ground and lower-ground floor flats’. They have it in mind that flats at this level will be dark and dreary, but I beg to differ,” says Shaun Macnamara, head of West End sales at CBRE Residential, which is marketing this basement flat for £2.85 million.

“This was often the case when botch-job conversions were made to period houses, but as residential square footage now commands such a premium, these unloved spaces are experiencing a change in reputation.”

Basement flats will also offer the best value for money. Savills finds that lower-ground and ground floor flats are the least expensive in prime London, with the square foot price 13.8 per cent and 14.5 per cent lower than the average, respectively.

The basement conversion is not just to be found in super-luxury schemes in central London. “We are doing them as far south as Balham,” says builder Billy Heyman, of BTL Property.