Being punched in the face without warning is the ultimate test of a spy. The involuntary response, usually shouted in one’s native tongue, can give the game away. Only the best trained operative can keep their cover, deploying a choice expletive in the language of their assumed identity.
So writes David Esdaile Walker, the Fleet Street journalist recruited as an intelligence operative for M15 before World War II who, it turns out, is a relative of mine. He learnt the test during training for the famed Special Operations Executive group, as Adolf Hitler was on the march across Europe.