Over the past two decades, London’s high-end property market was overrun by the global superrich led by Russian oligarchs who did so many big, brash deals that locals called the city Londongrad.

A mansion just a stone’s throw from Kensington Palace — on land leased from the crown — sold for $140m to one oligarch, while estates built by Victorian aristocracy and industrialists traded to Russia’s new rich, who added sprawling subterranean pools and sleek glass walls.