The number of teenagers arrested for terrorist offences has tripled in the last year, driven by the flood of British jihadists to Syria, figures show.
Some 46 youngsters aged 18 to 20 were held under terror laws last year, up from just 15 in 2013, and many will have been suspected fanatics returning from the war zone.
The lure of Isil is a growing concern as it continues to attract hundreds of British youths before brutalising and militarising them.
More than 700 Britons have gone to Syria and around half are believed to have returned.
Overall, a total of 289 people were arrested on suspicion of terrorism in 2014, a 30 per cent increase on the previous year.