It was not so much the pain from the stump on his shoulder — all that remained of his right arm — that troubled Ali Sher; the morphine had dulled sensation there. Instead, it was the terrible burns across his back and waist that caused him to wince with every movement.

“I wish you could stop the animals who burnt me from burning others, rather than just take my photo,” he gasped, wincing as he leant forward to show me his strangely discoloured, deeply pitted wounds, still giving off a chemical smell.

The 21-year-old Syrian Kurdish SDF fighter had until recently served alongside a unit of British special forces confronting Islamic State in Syria, and he recalled the British troops with a wan smile of…