I’ve only ever spoken to the Tory leadership contender Boris Johnson once. I was making a film for Channel 4 in the early noughties and wrote about it for the Spectator magazine, which he was editing at the time. Naturally we had a perfunctory conversation about education. His children had been at a primary school near where we were filming but, amid a lot of his trademark bluff and bluster, he admitted that sending them to state secondary schools was…