£90m home to set new record

The record for an existing British property is believed to be held by the Kensington Palace Gardens home of steel magnate Lakshmi Mittal, who paid about £57 million for it in 2004.

Only the penthouse in the as-yet-unbuilt One Hyde Park is said to have been sold for a higher sum - £100 million - but that was to the development's major investor, the Qatari foreign minister Sheikh Hamad bin Jassim Jabr al-Thani.

The six-storey stucco house in Belgravia, which is nearing the end of a two-year refurbishment, is one of the finest residences in a square dominated by embassies and offices.

Land Registry records show it is owned by a Madeira-registered company, believed to be run by a Lebanese man. The owner paid £6.87million for a 99-year lease in January 2005. The property was previously used as offices.

The conversion into a family home means it will have a basement swimming pool, gym and media room as well as garaging for four cars.

The property will have 12 bedrooms, including a master bedroom suite, 12 bathrooms, a "grand salon" and a lift - all over a total of more than 20,000 sq ft. There is also a mews house in the garden suitable for staff.

The refurbishment has been masterminded by Solland Developments, known for lavish schemes tailored for the Middle Eastern market.

The owner plans to ask for £90 million when the fully furnished house goes on the market early next year, according to property market sources. Two firms of estate agents have already been briefed.

Two years ago, a similar property in the square had an asking price of £33million when it was sold to Saudi sheikh Walid Juffali and his wife, former US supermodel Christina Estrada. Roman Abramovich's former wife Irina reportedly made an unsuccessful bid on a £35million house there.

A shortage of large, ambassadorial properties in central London has driven up prices. "Belgrave Square is arguably the grandest and most beautiful square in central London," says Phyllida Poltock of Henry & James. "The handful of buildings which are private residences are substantially bigger than most others in the area and make wonderful trophy homes."