When a tube train has the words NOT IN SERVICE on the front, you’re not supposed to get on it. That’s why I got on it.

Come on, it stopped and opened its doors right in front of me. They never do that when they’re not in service. It was late enough that there were only a couple of other people waiting, and they both heeded the tannoy’s orders not to get on the train. It was that officious tone echoing down the platform that clinched it. What could I do but the oppo...