When the two-week sharia course was over, most of the men were transported to another group of damp mountain caves a few miles away. They now started the military training class. Abu Ali, with his smoker's lungs, would just sit down on the rocks when he got tired.

The trainers shouted at him, and he would hold up his hand and shout back: 'I'm doing administration, not combat.' He was already getting a reputation as a laggard.

On the last day of the course, the men were summoned from their cave in the morning and asked to recite an oath of loyalty. Abu Ali found himself standing with about three dozen other men near a bus.

A Syrian commander in battle fatigues told them they were going to the frontlines in Iraq. 'Sir, I don't want to go to the frontline,' Abu Ali told the commander. 'They said I could do administration in Raqqa.'

The commander looked at him, stone-faced. 'You swore an oath,' he said. 'You must listen and obey now. The penalty could be death.' Abu Ali stood for a moment, registering the shock, then he walked towards the bus.

After a few days of travel, Abu Ali arrived in Garma, a village just west of Baghdad near the frontline.

He and another recruit dragged wounded men from the battlefield. It was terrifying work. They could hear and feel bullets whizzing past them in the pre-dawn darkness, and some of the men they dragged – there were no stretchers – were screaming in pain.

On the morning of the third day, Abu Ali and a new friend named Abu Hassan walked together into the headquarters in Garma and confronted the Iraqi commander.

'We don't want to fight any more. You are leaving dead and wounded men behind.

'The prophet Muhammad, peace be upon him, did not force men to fight against their will.' He knew he was taking a risk.

Abu Ali was packed on to a bus bound for Syria. The men on board knew they were likely to be punished. 

The tale of Abu Ali's life as a jihadi is published in autumn

Freedom, finally: When Abu Ali was moved to Tel Abyad he found himself next to an internet cafe and his WhatsApp messages pinged into life