Michael Bloomberg shows Sadiq Khan his company’s new £1bn headquarters in London. He visits the city every month, sometimes just for the day

Michael Bloomberg didn’t become the tenth richest man in the world and a three-term mayor of New York by mincing his words. Brexit was “the single stupidest thing any country has ever done”, he told a conference this month. “But then we trumped it.”

As we sit at his desk in Bloomberg’s vast new London headquarters, designed by Lord Foster of Thames Bank, I read that punchy quote back to him. “I did say that. Probably regret it,” he says. Really, you regret saying it? “No!” he says, forcefully. “It happens to be true, unfortunately.”

The man who ran New York for 12 years until 2013, considered running for president last year and has amassed a $48 billion fortune from his eponymous financial information and