Britain has prosecuted just ten per cent of foreign terrorist fighters who have returned from Iraq and Syria, highlighting the difficulty of securing battlefield evidence of crimes, a UK terrorism watchdog said.
The UK government estimates that a fifth of the 900 people who travelled from the UK to join the ranks of ISIS in Syria were killed while another two-fifths remain in the region.
But only about 40 of the 360 who have returned to the UK have been prosecuted, said Jonathan Hall, the independent reviewer of terrorism legislation.
“The dog that did not bark was the return of foreign terrorist fighters,” Mr Hall said in his first report published on Thursday. “Prosecutions remain the exception” for those who have returned from ISIS-controlled areas, he said.
Analysis of prosecutions suggested that only two returning fighters were successfully prosecuted in each of three years to 2018.
The low rates of prosecutions were partly because a large number who returned were in the earliest stages of the Syrian war and were not considered to be national security concerns.
Those who remain outside the UK includes "many of the most dangerous" who had been trained, indoctrinated and had a network of terrorist contacts, the report found.
The numbers of those prosecuted has led to disquiet among the allies of the UK.
The former US Attorney General Jeff Sessions told a Senate panel in 2018: “I have been disappointed, frankly, that the British are not willing to try the cases but intend to tell us how to try them and they have certain evidence we need.”
Mr Hall said the greatest challenge was to collect battlefield evidence, including forensic evidence from homemade bombs. Evidence collection was also hampered by the lack of infrastructure and police forces.
The government has responded to the difficulty of securing prosecutions by introducing a new offence punishable by up to ten years in jail if someone enters a designated terrorism hotspot. No areas have so far been designated by the government.