The British government is spending 50 per cent of GDP, but taking just 40 per cent in taxes. The coalition’s aim is to close that gap over the next five years (still leaving a massive accumulated debt, by the way), partly by raising taxes and partly by cutting spending. The hope is that economic growth will keep the eventual figure closer to 40 per cent than to 50. What, though, is the optimum share? The above video hazards an answer. The Rahn Curve is to state spending what the Laffer Curve is to taxation. Drawing on a mass of published...