Paul Dimoldenberg, leader of the Labour opposition in Westminster Council, said the situation had reached a “tipping point” and was starting to concern lawmakers.

“Some of the richest people in the world are buying property here as an investment,” he said. “They may live here for a fortnight in the summer, but for the rest of the year they’re contributing nothing to the local economy. The specter of new buildings where there are no lights on is a real problem.”

In its report, Savills found that in 2011-12, 34 percent of people buying residential properties in the resale market in prime areas of London — places like Kensington, Chelsea and Mayfair as well as Belgravia — were from overseas, up from 24 percent in pre-crisis 2007. In the most exclusive spots, foreigners accounted for 59 percent of the sales.

This has made parts of London more international, more expensive and more empty. The salesclerk at a Belgravia clothing boutique, who also spoke on the condition of anonymity because she did not want to get in trouble, said that at some times of the year the area was virtually abandoned. “We’ll shut for the whole of August,” she said.

Many foreign purchasers are buying to rent, said Naomi Heaton, chief executive of London Central Portfolio, which represents high-end buyers. “There is a definite concern about ‘lights out London,' ” she said, “but the reality is that half of what is bought is bought for rental.”

But not at the top end, said Yolande Barnes of Savills.

“The very wealthy won’t rent their houses out. Why would they?” she asked rhetorically. “It’s more like buying their own private hotel, really — an alternative to living in a suite at the Dorchester.”