I got Boris Johnson into trouble once, without meaning to. The two of us had been driven hither and thither across Uganda by Unicef in the back of an expensive Mercedes 4×4 to gaze at the fatuous projects they had delivered for the benighted natives. We had been chosen for the trip because we were perceived, rightly, to be unconvinced by the efficacy of some western foreign aid programmes and even less convinced — in my case, at least — by the UN.