Most homebuyers began to feel the icy grasp of the credit crunch in September when the banks reacted to the money market freeze by restricting lending. But for some househunters in London's smartest postcodes, these events were opportunities they were exploiting to boost the funds they were planning to lavish on real estate: one man's difficulty in obtaining a mortgage is another man's fortune from shorting the market in mortgage-backed securities.

Since September, the Sloane Avenue office of Knight Frank, the estate agents, has sold ten properties for “north of £10 million”. One of these homes, a £19.5 million duplex apartment in a block developed by Candy & Candy, offers air purification to its residents. But then the rarefied atmosphere of the property market in Belgravia, Chelsea and Mayfair has become even more of a microclimate, with international buyers apparently impervious to signs of an economic slowdown outside SW3.

Knight Frank says it needs more stock to offer disappointed bidders, as mansions are in scant supply. The level of demand is shown in the £26million sale price agreed late on Wednesday night by its Kensington Church Street office, for a large modern house in the area.

Tom Tangney of this office describes the house's facilities: “pool, cinema, concierge, 24-hour security, parking for four cars.” The current owner paid £13 million just three years ago.

This spending spree has bewildered many agents who were preparing themselves for a desultory Christmas. Jonathan Hewlett of Savills notes: “There is not as much caution as you expect — we've seen some phenomenal deals in the last few weeks at the very top end.”

He added: “Deals are also still going through in the market between £1 million and £4 million, which is where City workers with bonuses are the most active, although there's more due diligence going on than before, more dotting of the i's and crossing of the t's.”

The properties sold by Knight Frank's Chelsea office rank in expensiveness as follows: the £19.5 million duplex apartment in Manresa Road, Chelsea; a £15 million eight-bedroom family house in Cadogan Place, Belgravia; a £15 million house in Wilton Crescent, Knightsbridge; a £12 million apartment in The Knightsbridge, a lavish 21st century block minutes from Hyde Park and Harrods; an £11.5 million penthouse in Davies Street, Mayfair, above the Cipriani restaurant, and a £10 million Grade II-listed terraced house in Ovington Square, Chelsea, which was originally offered at £7.5million. The buyer may have been seduced by its history: Lilly Langtry, mistress of Edward VII, lived at this address.

Knight Frank would not specify the exact location of two £11 million new-build flats in Belgravia. Secrecy covers many multimillion-pound transactions, with some vendors anxious not to reveal that they are marketing their homes.

Wealthy foreigners are the new owners of almost all of these properties, but there is some doubt as to whether they will continue to be enthusiastic investors in prime metropolitan bricks and mortar in 2008, or decide to settle in fiscally forgiving Switzerland. Some individuals who are resident non-domicile in the UK, enjoying generous tax concessions, see the proposed introduction of a £30,000 annual tax as the beginning of the end.

For now, however, Mr Hewlett says that it is mostly advisers to the non-doms rather than the non-doms themselves who are perturbed. They suspect that the Government, despite its public protestations, would prefer to see the non-doms stay on in Britain.

Yesterday, Capital Economics which currently takes the gloomiest view of the prospects for the housing market in 2008, downgraded its forecast, saying that prices in the whole UK market will slide by 5 per cent and by a further 8 per cent the year after.

But this coincided with some good news for one moneyed person aspiring to move into Belgravia in 2008. Last month Andrew Langton of Aylesfords, the estate agents, sold a flat in a Belgravia block for £15 million, dashing the hopes of several dozen other bidders.

He has now found another willing seller in the block for the same sum, which means that there will be least one happy multimillionaire this week.