AS A rule, women behave better than men, or are less frequently caught out: they make up just 5% of Britain’s prison population. Even these troublemakers are gentler than the opposite sex. In 2014 eight in ten women prisoners were jailed for non-violent offences, compared with seven in ten male prisoners.

Behind bars, however, a different trend emerges. It is women who more frequently run up against prison rules. In 2014 there were 137 punishments doled out per 100 women but only 105 for every 100 men. They are also more violent, committing 52 assaults on staff per 1,000 female prisoners in 2015 whereas the male rate was 45. Why do women behave so badly in prison?

Diego Gambetta, a sociologist, says women make rougher inmates because they take longer to establish a hierarchy. Fighting, he says, “is an information-seeking device”, and although the toughest men sport large muscles and scars, the toughest women are harder to spot without a scrap. Another theory is that female prisoners are trickier to manage because they are more likely to suffer from mental illness: in 2015 26% of them (and 16% of male inmates) had had a psychiatric admission before going to prison. A third argument is that female jails are less crowded, so unruly prisoners are easier to spot.