The red-haired man in the queue behind us wore a pale turquoise cotton jumper and a sly look. I glanced down at his feet just as he shoved a 50p piece under the counter with his right toe.

It was the man’s turn to pay. While I was putting my change away, I overhead him complain to the cashier that she had short-changed him: he said that he had given her a £10 note, not £5.

Both TPR and I knew that the man was lying. We headed straight for a supervisor to report the crime. The man overheard us and confessed. The CCTV would show that he had been playing this devious trick on the canteen staff for weeks.