You could walk past No38 Gloucester Road without a second glance: after all, it is just another unremarkable front door sandwiched between an estate agency and an off-licence on a busy London street. But step through the door and through the dark, narrow corridor and you arrive in an extraordinarily light and airy wood-and-glass construction, an ultramodern home in the heart of South Kensington.

“It is one of the things I love about this property,” says Ivo Hesmondhalgh, a property developer and the house's current owner. “It's not too ostentatious. You are bang in the middle of Gloucester Road and no one has a clue that behind a very ordinary-looking front door lies one of the nicest houses in London.” He is not the only one who thinks so: the property is one of six London houses to receive a Royal Institute of British Architects (RIBA) award this year.

Designed by the architect Cezary Bednarski, of Studio Bednarski, the 3,790sqft house was built by Diamond Construction, a firm with which Hesmondhalgh has worked for 20 years. “When we purchased the property it was just a derelict warehouse. It took us two years to get planning permission and another four years to complete.” Initially, neighbours were concerned about the plans, fearing the erection of some ultramodern skyscraper, but once it become clear that Hesmondhalgh's plans were to dig down, rather than build up, permission was granted.

“I probably wouldn't have taken it all on if I'd known quite the level of stress it would entail,” Hesmondhalgh admits. “There were, for example, 20 different party wall agreements.”

So why, after all the work he has put in to building his first house, has he decided to sell? “We're selling because we're not exactly sure where we want to live,” he says. For the past five years he and his family have been living in Barcelona. “We have enjoyed the experience of living abroad, but we also want to keep a base here.” No38, which is rather too big to be just a base, is now for sale for £7.95 million.

At more than £2,000 a sq ft, it is expensive, even by South Kensington standards; its price tag is justified, Hesmondhalgh claims, by its rarity value. “There are just a handful of modern houses in Central London and they very rarely come up for sale,” he says. At its heart is a large, open-plan reception area: at one end is a library, at the other the kitchen and dining room. The main living space is in the centre, is glass-fronted and has a double-height ceiling. Beyond the dining room there is a TV room with a sliding door. A utility room and staff bedroom are also on the ground floor.

From the central living area two facing wooden staircases lead upstairs to the four main bedrooms, all of which face out onto the garden, and two of which are en suite. The master bedroom has a large terrace, while bedrooms three and four have doors leading out into the landscaped garden. Outside, there are two more wooden staircases leading up to the terrace and upper part of the garden. The finish is luxurious: worktops are not just any old granite, but made from fossilised limestone more usually seen in works of art. In the ceiling are not skylights but light “tunnels” that magnify and diffuse the light.

What strikes you is not just how light it is, but how quiet. Out in the garden, a few dozen feet away from one of London's busier roads, you cannot hear the traffic, largely because the house turns its back on the road. And despite its sunken position, it does not feel overlooked, except by trees. “If you open the windows, all you can hear are the birds,” says Hesmondhalgh.

Details: Knight Frank, 020-7938 4311

Explore Property

• Buying & Selling

• New Homes

• Overseas

• Interiors

• Investment

• Gardens

• Cool In Your Code

• Specials

Times recommends

• Analysis: frustration for everyone - except investors
• Spanish property: why it's crunch time on the Costa del Sol
• Buy-to-let: professional investors cash in on the credit crunch