Sheikh Hamad, the foreign minister of Qatar, is behind the purchase of a £100-million (Rs 850 crore) penthouse home overlooking Hyde Park, the most expensive flat in London.

The apartment is the biggest of 86 luxury flats in the ambitious One Hyde Park scheme, which is almost two years from completion.

A quarter of the flats in the building designed by Richard Rogers have been sold in the past few weeks, sources close to the scheme said.

It is thought that each flat is fitted with bullet-resistant walls and windows. There is underground parking for 115 vehicles and private lifts direct to each residence

The site will also have an underground passage to the nearby Mandarin Oriental Hotel, where 36 staff will be on hand to cater to residents’ needs.

The largest and highest of the penthouse suites has been bought with funds linked to Sheikh Hamad bin Jassim bin Jabr al-Thani, the foreign minister and first deputy Prime Minister of Qatar.

Two of the other penthouses have also been sold, property sources said.

Sheikh Hamad is a key financial backer for the construction of One Hyde Park. The scheme is owned and controlled by Project Grande (Guernsey) Limited, whose major shareholders include CPC Group Limited, a Guernsey-based investment vehicle owned by Christian Candy.

Earlier this year, The Times revealed that the One Hyde Park flats were on the market for £4,200 per square foot, which would have made the 20,000 sq ft penthouses worth £84 million.

But buyers of the best flats with views north over the park are understood to have paid £5,000 per square foot.

Prices of multimillion-pound homes and offices have been soaring in the capital, prompting warnings that parts of the market are overpriced and set for a correction.

Trophy properties valued at £5 million or more are now showing annual price inflation of 50 per cent, according to Savills, the estate agent.

It added that international property investors were continuing to buy up the smartest parts of Kensington, Chelsea and Knightsbridge.

Purchases by overseas investors of West End and City offices have also picked up sharply this quarter, according to research by Cushman & Wakefield, the international property agents.

Investors bought £2.6 billion of City offices in the first quarter. A third were foreign-fund buyers. This time last year, City office sales were at £2.3 billion, with foreign-fund buyers largely absent.

Harriet Black, of Savills, said: “London continues to attract wealth from around the world and we see no end to the strong demand for prime property.”