“It is a very easy way to launder money,” he says. “It is a way to legitimize dubious wealth and to do so on a very large scale, which is hard to do with other types of assets.”

Wealthy’s Idiosyncrasies

After 25 years spent selling premium real estate, de Keyzer has become increasingly attuned to the idiosyncrasies of the global wealthy. Middle Eastern buyers won’t consider houses without elevators. Singaporeans require lots of staff accommodations. Russians, on the other hand, have few servants and consider privacy and security paramount. Indians like his- and-her walk-in closets. Americans tend to window-shop, preferring to rent for tax purposes.

Potential buyers sometimes phone de Keyzer directly. More often, inquiries are conducted through intermediaries: private bankers, lawyers, personal assistants -- and, increasingly, buying agents. These specialized consultants market themselves as free from conflicts of interest because, in the U.K., brokers such as de Keyzer are paid by the seller.

Restrictive Rules

De Keyzer regards their growing ranks with ambivalence. Some lack qualifications and neglect to tell clients about the U.K.’s restrictive rules on modifying historic properties, or that what’s being “bought” is often in fact a long-term lease from the estate of an aristocratic family, such as the Grosvenors or the Cadogans, who own much of central London.

The best buying agents, however, help screen potential purchasers, particularly for their financial wherewithal.

“We don’t want time wasters,” de Keyzer says.

The principals, as the buyers are known, get personally involved at some point. They always view the house at least once, de Keyzer says. Even for a billionaire, £10 million and up is a sizable chunk of change. The viewing, however, may not last long: De Keyzer once watched a German billionaire buy a £25 million house in Chelsea after a single 15-minute showing.

While they may own property elsewhere, many shopping for super-prime -- particularly above the £25 million mark -- are neophytes when it comes to London.