In a desolate expanse of north-east Syria, where there is little more than dirt and dust, the sprawling Al-Hol camp rises from the desert.

Hot and dry in summer, with relentless winds whipping up sandstorms, and exposed to biting cold in winter, the high-security facility is hemmed in by metal fencing and patrolled by Western-allied Kurdish-led troops.

Behind the barbed wire, under the eyes of surveillance cameras and watchtowers, is the largest single remnant of the bloody caliphate once ruled by Isis. The camp is home to thousands of women and children, the relatives of the terror group’s legions of male fighters, the majority of whom are held at an unknown number of prison facilities spread across the region.

Among those facing indefinite detention in Al-Hol, the smaller Al-Roj camp farther north and the secretive jails are a number of terror suspects linked to Britain – including Shamima Begum and “Jihadi Jack” Letts – who travelled to Syria and Iraq to join Isis between 2012 and 2019. Some 20 British women, 40 children and 10 men are believed to be held in facilities across the region in total.

The fate of the prisoners has been the subject of years of concern and debate following the fall of Isis’s caliphate six years ago. To this day, foreign governments and the Kurdish-led Syrian Democratic Forces (SDF) continue to wrestle with the complexity of finding a long-term solution to the security problems they pose.