I discovered that life in the camp was based on a few simple, fundamental rules. They relied on terror, intimidation and constant surveillance on all sides. The different groups held one another in check.

The ‘infidels’ – the ones who had originally been Christians and were now supposed to have converted to Islam – occupied the lowest rung in the pecking order. We women and girls were effectively the slaves of the camp and had to do all the lowly jobs: fetching water, collecting wood, keeping the camp clean.

We had no rights, and anyone could treat us exactly as they wished. There were no infidel men among the prisoners: I assumed that most of them had been killed. Only men who immediately joined the group had any chance of survival. The ‘Muslims’ – those who had been Muslims in their earlier life, or who were considered to be converts and now had to prove themselves as new members of the group – were a rung above us.

The women in this category had each been assigned to a different Boko Haram fighter as ‘wife’. They were seldom seen, since according to the strict programme of the sect they were entirely devoted to the physical wellbeing of their husbands. In their part of the camp there were a few walls made of plastic sheets to protect them against the eyes of the others when they had to perform their duties.

The Muslim men who already had some fighting experience were our guards; some of them were very young, perhaps even younger than me. They could earn special laurels for themselves if they treated us very severely. Their cruelties were sometimes breathtaking.

When they behaved like that they were probably trying to impress the long-serving members of the sect. On the other hand, if they earned a reputation for treating us too carefully, they themselves risked falling into disfavour.

The Boko Haram fighters closely observed the behaviour of the newcomers in the group and even kept a record of it. Their regime of terror extended into their own ranks: there was no room for fighters with scruples or any kind of inner inhibitions. Only those who took real pleasure in murdering and torturing ‘infidels’ were considered ‘true’ Muslims, and could go on living amongst them in the long term.

All others ended up on a blacklist. A list that could only mean a death sentence. So everyone in the camp – from those at the top to those at the very bottom – was acting out of fear, constantly trying to protect their own lives.

Exclusive: young mother who escaped Boko Haram shares her story