‘Why did you leave us?’ said the old Sudanese man in Omdurman market. ‘Things were so much better when you were here.’ He was talking about the British empire, of course, and apologies if I’ve told the story before, as I know I have. It’s just that it’s such a fantastically satisfying way of winding up all those guilt-ridden post-colonial types who find it a source of shame and embarrassment that the world’s atlas was once half-covered pink.