In a café in Norfolk last week, my seven-year-old son uttered words that mortified me. No, he didn’t comment loudly on someone’s weight, or ask why the lady next to us had a moustache. It was worse than that. Asked by a kindly man at the next table if he was enjoying his bacon sandwich, he declared to the café at large: ‘Yes, but I prefer them with rocket!’

Judging by the gentleman’s slightly blank smile, I’m not sure if he even knew what rocket was, let alone that in the London suburb where I live, it’s now as much a...