Three years ago, our daughter had to catch a cheap, 1am flight from Stansted. The whole family drove her to the airport, and even got chips from the drive-thru McDonald’s on the way. We know how to have a good time.

However, as we drove through north London – Highgate, Barnet, Edmonton, Brent Cross – something started to make me feel odd. There was something wrong about what I was seeing, but I couldn’t, at first, put my finger on it. It was 11pm, on a Friday in July – the streets in the suburbs were reasonably busy with people walking home from restaurants, and pubs; or walking to friends’ houses. It was a hot night. People were enjoying the summer.