There is no pleasing some people. During the 1960s and 1970s, the wealthy fled the west’s big cities to escape crime and urban blight. In the US it was known as “white flight”. Cities such as New York and London were in headlong fiscal decline.

Then came the great revival — or the “reverse white flight”. Today London and New York are the world’s metropolitan hubs. Aspiring global cities strive to copy them. Yet success has bred a new kind of problem: economic segregation.

In his latest book, The New Urban Crisis, Richard Florida bemoans the divides within the “winner takes all” super-cities of the 21st century. Having come back from the brink of bankruptcy, they are now succeeding too well. Soaring property values are turning the west’s largest metropolises into walled-off playgrounds of cosmopolitan elites.