To those of us who are not professional economists, the current tiff concerning the details of the RogoffReinhart/public debt slowdown thesis looks increasingly like yet another demonstration of the questionable relevance of the dismal scientists.

Much more significant is the fact that, unless they return rapidly to sustained and strong growth, Spain and France will, within three years, join Italy in the club of those countries whose public debt exceeds 100 per cent of their gross domestic product. At this level, if your growth is less, even slightly, than the rate you pay to roll over your debt and if you are unable to avail yourself of devaluation, you have passed the event-horizon leading to eventual default.