Through the keyhole at world's first £100m flat

The computer-generated picture visualises the £100 million One Hyde Park penthouse, the most expensive flat in the world, upon completion in 2010.

Other homes in One Hyde Park, Knightsbridge, have already sold at record prices of £6,000 per square foot.

Russian oligarchs, oil barons, Saudia princes and A-list stars are among those said to be buying the Candy brothers apartments.

Managed by brothers Christian and Nick's development company Candy & Candy, the project features 80 flats designed by architect Richard Rogers with communal spas, squash courts and a private wine-tasting facility.

The most expensive penthouse apartments will feature bullet proof windows, purified air systems and "panic rooms" and everyone on site will have access to an underground passage leading to the nearby Mandarin Oriental hotel.

Half of the units have already been sold at an average of more than £20 million each with average per square-foot prices hitting £6,000 this year.

The figure dwarfs London's earlier record struck last June when a newly converted flat stretching across the first and second stories of two Regency houses in the nearby Lowndes Square, Belgravia, sold for more than £4,250 per square foot. A consortium - of which Christian Candy's offshore development company CPC owns a third share - bought the One Hyde Park site for £150million in 2004 when it was occupied by the rundown Fifties office block Bowater House.

Knight Frank's head of residential research, Liam Bailey, said sales at One Hyde Park proved the super-prime property market was still strong.

He said: "One Hyde Park is the most prominent example of activity at the top of the market, but its performance is not an anomaly. The pull effect of One Hyde Park has meant that whereas £2,500persqft represented the peak of the market in Knightsbridge in 2006, 18 months later £4,000persqft is not only achievable, it is now expected for refurbished and newly developed properties in the super-prime sector."

The biggest group of buyers are Russian, making up a third of the total. A quarter of buyers are Middle Eastern, 20 per cent are British and the remaining 22 per cent is split equally between the European and American markets.

Nick Candy said: "We are not surprised by the variety of purchasers at One Hyde Park; it is a truly international development and is representative of London's status as the global capital of the world."

At the end of last month the Candy Brothers sealed Britain's most expensive home property deal when Chelsea Barracks, located between Sloane Square and the Thames, was bought by the Qatari government and the Candy brothers for £959 million.