When he stepped down as head of the US futures regulator this week, Walt Lukken was mindful of the physical toll the financial crisis took on him last year: he says he lost 20 pounds in body weight in the months surrounding the Lehman Brothers collapse.

“I’ve put it all back,” he says, with obvious relief on a visit to London. Yet Mr Lukken recognises this should not elicit any sympathy. As calls grow for a new charter to be drawn up for the way the US – and the world – oversees financial services Mr Lukken admits regulators dropped the ball in not asking enough questions even as markets appeared to be functioning well.