Teenagers who “naively” travelled from Britain to join Islamic State in Syria should be given space to reintegrate into society on their return rather than be prosecuted, Britain’s anti-terror watchdog said today.

Max Hill QC warned against “losing a generation” of young men, and some women, by putting them through the courts after having being lured to go to the warzone by IS propaganda.

He spoke out a day after EU Security Commissioner Julian King said up to 8,000 foreign fighters in Syria and Iraq may return to Europe after the fall of the IS stronghold of Raqqa.