Anderson says the pervading sense of the country being “over the worst” when he started his role in 2011 was a “false dawn.”
Mr. Anderson also said efforts to define extremism as part of proposed new Government measures may prove an “impossible task”.The independent reviewer of terrorism legislation, who is due to leave his role, which he has held since 2011, next month, added strong intelligence is the key to avoiding an attack.
“What we see now is not more people being killed in this country – we’ve been both lucky and skilful in that regard over the last 10 years,” he said.
About 850 Britons are thought to have gone to fight in Syria with jihadist groups, including Islamic State (IS, formerly ISIS/ISIL). More than 100 have been killed, but around half returned home after experiencing battle.
Anderson, who is to leave his role next month, said:
“We’ve seen a lot of people return from Syria. About a quarter of them have been prosecuted, and only a few have engaged in the terrorist activity of any kind in this country, as far as we know.
“But we have to remember the people who have returned already were not necessarily the most committed fighters and that hundreds of Britons remain in that theater.
“When IS is defeated and loses its territory, as I’m sure at some stage will happen, they will be looking for somewhere else to go, whether that’s back to their home countries or somewhere else in the world.”