Residential conveyancing solicitors in London who handle high-value property sales will be watching One Hyde Park, the world's most expensive housing development, with interest.

The four Knightsbridge blocks, which overlook Hyde Park at the back and have been developed by brothers Christian and Nick Candy and a company owned by the Qatari prime minister, were unveiled officially at a glamorous launch party.

Although prices start at £6.5m for a one-bedroom flat and rise to £140m for one of the penthouses, it is believed more than 60% of the prestige living spaces have already been sold, mostly to foreign businessmen from the Middle East, Asia and Russia.

Facilities for the residents of the 86 sumptuous flats include a cinema, swimming pool, saunas, gym, virtual games room and a golf simulator. Private access to the neighbouring Mandarin Oriental hotel will enable its staff to respond to requests 24 hours a day.

A representative of the lead estate agent, Savills, said, "We've had strong interest from clients around the world. The launch has been extremely successful and resulted in around 60 bookings for viewings next week. This is the best residential development in the world, and the international interest, in particular, is very strong."

Averaging about £6,000 per square foot, the price of the apartments is believed to be the highest in the world and the number of successful residential conveyancing contracts signed at the prestigious address will be seen as a barometer of the continued attractiveness of property sales in London, especially for the super-rich.