The size of the alleged Bernard Madoff scam, if it lives up to its initial $50bn billing, is astounding, yet unsurprising. History tells us that bubbles spawn swindles. After the biggest credit bubble of all time, we now may have the biggest swindle of all time. As so often, the real mystery is how such a big fraud could have been built on so flimsy a base.

This was, after all, a hedge fund that delivered implausibly consistent, and consistently good, returns. These were verified by a firm of auditors employing all of three people. Mr Madoff dealt through his own in-house broker, raising questions about custody of assets and internal control. Many experts felt the options trading strategy he claimed to pursue could not have generated such returns with so many billions under management. Why were professional as well as private investors taken in?