On Wednesday last week, yields on 10-year US Treasuries – generally seen as the benchmark for long-term interest rates – rose above 3.73 per cent. Once upon a time that would have been considered rather low. But the financial crisis has changed all that: at the end of last year, the yield on the 10-year fell to 2.06 per cent. In other words, long-term rates have risen by 167 basis points in the space of five months. In relative terms, that represents an 81 per cent jump.

Most commentators were unnerved by this development, coinciding as it did with warnings about the fiscal health of the US. For me, however, it was good news. For it settled a rather public argument between me and the Princeton economist Paul Krugman.