“It presents itself as an apocalyptic movement, talking about the end of days, the return of the caliphate and its eventual domination of the world,” said Hassan, who lives in Abu Dhabi where he works as a researcher for a think tank.

“These beliefs are not on the margins — they are absolutely mainstream. They are preached by mosques across the world, particularly in the Middle East.

“ISIS takes these existing beliefs and makes them more appealing by offering a project that is happening right now,” he said, using an alternative name for IS.

Hassan’s research along with co-author Michael Weiss — a US-based journalist — gave them a rare insight into IS training camps for new recruits, which vary in length from two weeks to one year.