Young Britons returning from Syria after becoming disillusioned with Islamic State (IS) could be a used as powerful deterrent to dissuade others from going to join the extremists, a former intelligence chief has said.
Nigel Inkster, a former assistant chief of MI6, said the authorities needed to be able to identify "dangerous extremists" who could pose a terrorist threat if they were allowed back into the country unchecked.
But speaking at the International Institute for Strategic Studies think tank in London - where he is now director of transnational threats and political risk - he said it was important to distinguish them from young people who had simply found themselves "out of their depth" and who could have a "powerful inoculating effect" on others who were thinking of going.
"I think the British Government does recognise that there is a need to distinguish between misguided young men and women who have got out of their depth but not actually done anything that drastically wrong versus dangerous extremists from whom the public needs to be protected," he said.
"Young people who come back from Iraq and Syria and who are prepared to tell their peers 'It isn't as you think it is and you don't want to go there' potentially can have a powerful inoculating effect.
"The Government are well aware of this but at the same time they are right to feel that there needs to be some sort of triaging mechanism that does begin with being able to bring these people into a system and exercise some control over them."
His comments came after ministers yesterday tabled the new Counter-terrorism and Security Bill, which includes powers to block suspected British fighters from returning to the UK.
Mr Inkster acknowledged that the meteoric rise of IS meant its appeal to elements of the Muslim community around the world had overtaken that of more traditional jihadist groups like al Qaida.
"It is an ideology and a doctrine that is guaranteed to attract people with psychopathic tendencies," he said.
However he said that many Britons and other Westerners who joined IS found themselves being used simply as "cannon fodder" or being allotted "relatively menial" tasks like guard duty.
While groups such as al Qaida in the Arabian Peninsula may have passed on bomb-making techniques to IS, Mr Inkster said that its methods were very different to the older jihadis who had an "obsession" with mass casualty attacks like 9/11.
"What we haven't seen, that I am aware of, is any evidence of the structured attack planning directed from some central entity that we did see during the previous decade with al Qaida based in the tribal areas of Pakistan," he said.
"What they are now doing is planning to just go out onto the street and beheading individuals at random. This makes for a much more challenging security environment because there is a lot less for security services and police forces to get across in terms of disrupting this kind of behaviour."
He said that IS had antagonised some of the more traditional jihadis by the speed with which it had declared an Islamic "caliphate" in the territories it has taken in Syrian and Iraq and that, ultimately, it may overreach itself.
"All of these groups do carry within them potentially the seeds of their own destruction," he said.
"I think there is a very strong possibility that IS may, in due course, run out of steam. Not to the extent of disappearing, but to point of where it simply represents one phenomenon in a much more variegated pattern of global jihadism."