Suppose that at some time in 2006 – or, more usefully, earlier – the UK Financial Services Authority had written to the banks it supervises about the explosion of structured credit products. They might have said that the practice endangered their balance sheets and financial stability more generally. Suppose the FSA had then insisted that banks substantially reduce the exposure to these markets. With hindsight, this judgment would have been entirely justified.

Yet would these banks have accepted this opinion? Or would there have been the political and press reaction that has greeted other means to tax or rein in the City of London’s activities?