One day, on their way back from dinner in Washington DC, Leslie Meltzer and her husband Tyce Palmaffy saw something dreadful. They were stopped at traffic lights watching a man slowly cycle towards them, when suddenly another man came out of nowhere and knocked the cyclist over. Then he began stabbing the cyclist as he lay on the ground.

I thought of this story when, last week, it was reported that the former defence secretary Gavin Williamson had sworn on his children’s lives that he was innocent of leaking the proceedings of the National Security Council. It seemed such an odd thing to say. What could possibly explain such vehemence?

Well, the first possibility is that Mr Williamson is just a rogue. He knows full