Max Hill QC - seen outside the Old Bailey in June 2015 - said hundreds of Britons coming home after serving under the brutal terror group in Iraq and Syria have not been charged to avoid 'losing a generation' of young men

'Naive' teenagers who return to Britain after fighting for ISIS should be allowed to reintegrate rather than face prosecution, according to the anti-terror watchdog.

Max Hill QC said hundreds of Britons coming home after serving under the brutal terror group in Iraq and Syria have not been charged to avoid 'losing a generation' of young men.

Around half of the estimated 850 UK citizens who joined ISIS in the Middle East have since returned, according to official figures.

Mr Hill, the independent reviewer of terrorism legislation, told BBC radio: 'The authorities have looked at them and looked at them hard and have decided that they do not justify prosecution, and really we should be looking towards reintegration and moving away from any notion that we are going to lose a generation due to this travel.

'It's not a decision that MI5 and others will have taken lightly.

'But they have left space, and I think they are right to do so, for those who travelled out of a sense of naivety, possibly with some brainwashing along the way, possibly in their mid-teens and who return in a state of utter disillusionment and we have to leave space for those individuals to be diverted away from the criminal courts.'

The comments came a day after EU Security Commissioner Julian King revealed that up to 8,000 foreign fighters may come back to Europe after the fall of Raqqa.

Experts say those who stayed are now likely to head for Turkey in the hope of travelling on to Europe to seek revenge for the destruction of the caliphate.

Tory MP Geoffrey Clifton-Brown criticised Mr Hill's stance, saying: 'We should take a tough approach on this.

Around half of the estimated 850 UK citizens who joined ISIS in the Middle East have since returned, according to official figures. Pictured: British teenagers Amira Abase, Kadiza Sultana and Shamima Begum walking with luggage at Gatwick Airport to join ISIS

'Protecting against any future terror attack must be the primary concern.'

Supporting a terrorist group such as Islamic State is a criminal offence in the UK.

Earlier this week the head of MI5 warned Britain is facing the biggest terror threat of his 34-year career.

Andrew Parker said extremists are mounting deadly terror attacks with just a few days of planning as the UK sees a 'dramatic' jump in the scale and pace of the threat.

In his annual 'state of the union' assessment of the threat facing the UK, he said extremists are exploiting 'safe spaces' online, hindering intelligence efforts to root them out.

And he issued a fresh challenge to technology firms, saying they have an 'ethical responsibility' to help governments confront the threat.

His stark warning comes after Britain was hit by five terror attacks this year - killing dozens and injuring hundreds more.

The comments came a day after EU Security Commissioner Julian King revealed that up to 8,000 foreign fighters may come back to Europe after the fall of Raqqa(pictured after falling to Syrian forces on October 19)

Tom Wilson, of security think-tank The Henry Jackson Society, said: ‘Clearly these returning Islamic State fighters pose an unimaginably serious threat.

‘These are individuals who have not only chosen to join a terrorist organisation, but who in many cases will have been responsible for perpetrating atrocities … There is a very clear moral duty to bring such people to justice.

‘To pretend they can simply be reintegrated into British society not only shows a terribly naive misunderstanding of the jihadist ideology … but also a reckless disregard for the wellbeing of everyone else in British society.’

Security expert Professor Anthony Glees, of Buckingham University, branded Mr Hill’s comments ‘deeply disturbing’. He said: ‘Every person who has gone to fight for Islamic State is potentially a jihadist with a cause.

‘To believe otherwise is totally naive, not a good place to be for a reviewer of counter-terrorist legislation. Most decent Brits … believe those who went off to fight for IS [and] swore allegiance to it forfeited any right to return.’