Do people slip into cruelty by accident, or choose it for a cause?

According to the BBC Prison Study, it is much more the second than the first. The programme grew out of the 1971 Stanford prison experiment, in which students were recruited as prisoners and guards to test how people conform to roles. In 2002 the psychologists Steve Reicher and Alex Haslam ran their own prison study for a BBC documentary series. Fifteen men were randomly selected as prisoners or guards in a simulated prison over eight days. Unlike at Stanford, the guards were not told how to behave, only to work out how to manage a prison.

The results were very different. There was no evidence of guards conforming "naturally" to their role. When the prisoners were given a stronger sense of shared identity, they increasingly resisted, and on Day 6 a breakout made the guards' regime unworkable. A self-governing commune followed, but it collapsed under internal tensions. Then a group of participants wanted to install a much harsher regime, like the one seen at Stanford. Signs that it would harm participants ended the study early.

Reicher and Haslam's argument is that people move toward tyranny only once they identify with a group and its leadership, and once an authoritarian agenda has come to define that group and to be seen as a solution to its problems. They think this is what happened at Stanford, where Philip Zimbardo, as prison superintendent, explicitly encouraged the guards to demean prisoners.

Zimbardo disagreed. He called the BBC study simply reality television, with participants playing for the cameras. In 2018, though, he, Reicher and Haslam signed a joint statement that both experiments were valid and that behaviour in all participants could have been caused by more than the situation.