Of all the world’s capital cities, London stands out as a magnet for the super-rich.

Along Lancaster Gate, a 350-metre stretch of 19th-century stuccoed houses that traces the north of Kensington Gardens, non-UK nationals have snapped up almost 150 properties worth more than £500m.

The same is true in Eaton Place, a mile or so to the south-east, traditionally home to aristocrats and Oscar-winning actors, and now host to a largely international band of financiers and hedge fund managers.

Yet London is not unique in this respect. “There is a mobile urban elite who purchase, collect and periodically inhabit apartments in New York, London, Paris and Hong Kong,” says Earle Arney, chief executive of Arney Fender Katsalidis (AFK), an architecture and interior design firm.

“They are incredibly discerning buyers and the amount they invest in apartments is significantly, stratospherically different from the rest of the market,” he adds.

When the financial crisis hit in 2008-09, the property market stuttered and fell, but it quickly recovered. London Property Partners, an estate agent network, reported that 85 per cent of property sold in 2012 by its agents went to foreign buyers.

The market for super-prime properties has since reached new heights. Witanhurst in Highgate, the capital’s second-largest home (after Buckingham Palace), was reportedly sold for £50m a few years ago, but is expected to be worth £300m once refurbishments are completed.

New York reports similar froth. Prices for flats in the recent crop of skinny new skyscrapers are fast closing in on the $150m barrier.

But is the market sustainable — and where can investors still find, if not bargains exactly, then property likely to continue to rise in value?

Opinion is divided on the first question. Yes, the market will continue to grow over the long term, argues Mykolas Rambus, chairman of the Global Investor Immigration Council. Even given recent events in Chinese stock markets — and the fallout that has been felt around the world — he is confident that prospects remain positive. “In 2008-09, those who had enough dry powder saw it as a buying opportunity,” he says. “So this time around, [the events in China] might make them consider Singapore, London or New York in a more positive light.”

Wealth-X, the data provider that tracks the super-rich, estimates there will be 4,000 billionaires by 2020 — up from 2,600 today. All that money, as Mr Rambus points out, has to go somewhere.

However, Jonathan Gordon, director at IP Global, a property investment company, notes that prime central London — a barometer for the global luxury residential market — has appreciated by less than 2 per cent over the past year.

Where to invest becomes trickier still. Beyond the prime cities of New York, London, Tokyo and Singapore, location becomes less about investment and more determined by social or cultural factors. In an informal survey of 20 luxury residential consultants and agents, Berlin and Barcelona were cited frequently — for different reasons. Both score highly within Europe on the Economist Intelligence Unit’s Global Liveability Ranking, with Berlin seventh, and Barcelona in 17th place (London is at 26th, two places below Manchester).

Berlin is “a tier one city at tier three prices”, says Mr Gordon, “a hangover from reunification”. Silvio Pagliani, president of LuxuryEstate.com, notes that the German capital has also “experienced steady growth through periods when other cities were losing their stability”.

Apartment prices in Berlin rose by an average of 10.1 per cent in 2014, says IP Global, which estimates there will be at least 250,000 new residents by 2030.

Barcelona, on the other hand, is all about “quality of life”, says José Caireta, co-founder and managing partner of Squircle Capital, a property investment firm. Many clients have bought in London and Paris, he says, and are now looking at secondary markets.

In the US, activity remains centred around the four traditional wealth hubs of San Francisco, Los Angeles, Florida and New York. In Miami, says Steven Weilbach, senior managing director at Cushman & Wakefield, interest is driven by “folks from the southern hemisphere”. Also, perhaps unsurprisingly because of geography, it is predominantly Asian buyers who are snapping up properties along the west coast.

The nature of what the wealthy are buying is also changing. Off-plan purchases — buying on the basis of plans for an as-yet-unbuilt property — has become “preplan”, says Christopher Murray, managing director of London-based W1 Developments.

“Very wealthy people are approaching developers direct, buying an idea and hoping they get planning consent,” he explains.

But sustained demand has led to a boom in supply and consultants warn that while the super-prime market may survive and thrive, the tier just below — of houses and flats selling for £1m-£2m — is fast reaching overcapacity.

“There could be a bit of a bloodbath,” warns Mr Murray, “particularly in the high-density areas [in London], where there is a tonne of development coming on at the same time. Everyone is chasing the same customer.”

Hugo Greenhalgh, FT (​September 16, 2015}