In their fascinating book, Mistakes Were Made (but not by me), psychologists Carol Tavris and Elliot Aronson describe the classic study in which researchers infiltrated a group of people, led by a woman named Marian Keech, who believed the earth was going to be destroyed by a flood on December 21 1954.

While some of Ms Keech’s followers waited at home in despair as midnight approached on December 20, many others had rid themselves of their belongings and joined Ms Keech to await the flying saucer she promised would whisk them to safety.