– The Economist – “When the facts change, I change my mind. What do you do, sir?” asked John Maynard Keynes. David Cameron might feel like quoting the great economist when he tells Parliament, as now seems almost certain, that the government is reversing its decision to buy the aircraft-carrier version of the Joint Strike Fighter, the F-35C, rather than the F-35B variant originally ordered by Labour in the 1990s.