I was once a schoolteacher in England, where it was drummed into us during training that it was wise to join a teachers’ union, lest one of the students, in revenge for poor grades, falsely accuse us of impregnating them behind the bike sheds during lunchtime. But which particular outfit to join? Certainly not the NUT (National Union of Teachers), the nation’s largest and most militant teaching union, whose name was apt: the far-left group contained more nuts than a constipated squirrel.