Allowing Shamima Begum to return to the UK would not be a “moral exoneration” for her, the terror watchdog said.

Jonathan Hall KC, the reviewer of terrorism legislation, said he understands people wanting to see “vengeance” and “punishment” in relation to British citizens who joined so-called Islamic State (IS).

But he insisted the position now is different to the “real dilemma” the Government faced at the time her citizenship was revoked.

He said there was then a risk of an “overwhelming” influx of UK-linked jihadists following the collapse of the group’s territorial control of parts of Iraq and Syria.

And he said failing to permit her to return could lead the UK to be an “outlier” in Europe and prompt some to use the situation to brand the camp where she is held as “Britain’s Guantanamo”.

Ms Begum was 15 when she travelled from Bethnal Green, east London, through Turkey and into territory controlled by IS in 2015, before her citizenship was revoked in February 2019.

She has been locked in a legal battle ever since. Last week the 23-year-old lost her latest challenge against the decision to strip her of her British citizenship on national security grounds.

The Special Immigration Appeals Commission (SIAC) found there was a “credible suspicion that Ms Begum was recruited, transferred and then harboured for the purpose of sexual exploitation”.

However, the tribunal said this did not prevent the then-home secretary Sajid Javid from removing her citizenship.

Ms Begum – whose case has prompted huge debate – is reportedly one of an estimated 60 British women and children held by Kurdish authorities in Syria who have no means of leaving without the UK Government’s co-operation.

Mr Hall told Times Radio on Wednesday: “If she was to be brought back in it wouldn’t be saying anyone approves of what she did.

“It would be saying, taken as a whole, is the UK so much worse off than other countries that we have to leave our UK-linked individuals there?

“It makes my blood boil to think about what people did and I can really understand why the Shamima Begum case, in particular, has really become about her and her morality – or her lack of morality – whether she is lying now etcetera,” he added.

But there are risks in failing to repatriate people, the barrister said.

He said: “Several years ago the Government did have a real dilemma which was that a lot of UK-linked people, who on the face of it had the right to come into the country, if they had all come at once – let’s say tens, hundreds of UK-linked jihadis had come into the country – that would have risked overwhelming the system.

“You can already see people talking about Europe’s Guantanamo and if it was only Britain who had its UK-linked individuals in camps you can immediately imagine people trying to make a propaganda effort saying Britain’s Guantanamo.”

Mr Hall said he has a “hunch” the UK will in time make the political decision to repatriate them.

He said “I’m not just looking at Shamima Begum, I’m looking at the numbers who are currently in camps who are either UK citizens, and there are some of them, or people who used to be UK citizens and have been deprived, and we know that there are about 60 children who are UK-linked, slightly fewer than that (are) women and an unknown number of men.

“I’m looking at the position now when our allies – France, Australia, Sweden and Germany – are slowly bringing back their citizens and I’m just posing the question whether or not the UK is going to be a complete outlier.

“I’m posing the question: Is the UK really in such a bad position compared to our allies that we can’t in time absorb these individuals as well?

“If it’s going to happen, particularly bearing in mind the fate of children, probably better to do it now than wait even more years.”