A few years ago, Ron den Braber, an outspoken Dutch mathematics geek, was working in the risk department at Royal Bank of Scotland when he became alarmed about the models being used to price collateralised debt obligations.

Most notably, he concluded that the so-called Gaussian Copula approach then in use at RBS (and many other banks) significantly underplayed risks attached to the most senior pieces of debt - creating a danger of future, large losses.