But not by much: only by £8.9bn. If that number rings a bell, it is because this is the much-vaunted, but not much understood, "headroom" figure a lot of people in Westminster like to drone on about.

T he Audi R8 arrived on the scene in 2006 like a left hook out of nowhere. Its usual rivals, BMW and Mercedes-Benz, had no answer to this mid-engined all-wheel-drive sports car, s ...