A pair of boy’s white gym shorts and a lone plimsoll lie muddied and abandoned on the ground. A broken skipping rope hangs on the wall next to a painted black flag of the Islamic State of Iraq and the Levant.

The underground Isil training camp for children is every bit as macabre you would expect.

The Telegraph was given a tour of a “Cubs of the Caliphate” camp recaptured earlier this month by the Iraqi army, who say it was used to teach young recruits to become fighters for the jihadist group.

Built in a disused railway tunnel, part of a line which in more peaceful days connected Berlin to Baghdad, it is thought to have been the largest Isil training facility in Iraq.