Britons returning from Islamic State are likely to have acquired “potentially very dangerous” skills and connections, the head of MI6 has warned.
Alex Younger, who did not comment specifically on the case of runaway schoolgirl Shamima Begum, said UK nationals have a “right” to come home but that public safety was the first priority.
Meanwhile, Home Secretary Sajid Javid warned he “will not hesitate” to prevent the return of Britons who travelled to join IS.
Mr Younger told reporters at the Munich Security Conference: “They are likely to have acquired both the skills and connections that make them potentially very dangerous and also experienced extreme radicalisation, either in their journey to that place or when they are there. That fact needs to be uppermost in our minds.
“As we approach this admittedly extremely complex and difficult problem, public safety is the first thing that we will consider.
“It follows from that that anyone who has put themselves in this situation can expect to be questioned and investigated and potentially prosecuted if they return to our jurisdiction.”
The head of Counter Terrorism Policing, Assistant Commissioner Neil Basu, said: “Anyone who returns from Syria or other conflict zones, having gone in support of any proscribed terrorist group – whether that’s fighting for or against Daesh – or for any other illegal purposes, can expect to be investigated by the police.
“Any investigation is carried out with an open mind and based on the evidence available. This is to determine if individuals have committed any terrorist or other criminal offences, regardless their motivation, and to ensure that they do not pose a danger to the public or the UK’s national security.
“There can be no hope of repatriation without these investigations taking place, and anyone who does return to the UK from conflict zones can, at best, expect to live under stringent limitations set out in the Terrorism Prevention and Investigation Measures (TPIM) Act.
“We as a society must learn that we can stop this from happening in the first place by trusting our Prevent strategy, reporting our concerns early and stopping people being radicalised, investigated and, most likely, criminalised by the poisonous rhetoric spewed by terrorist organisations of any ideology.”
Mr Javid said those who left the UK to join IS were “full of hate for our country”, while security minister Ben Wallace warned that runaways who now want to come back must realise that “actions have consequences”.
Ms Begum’s family have pleaded for the 19-year-old, who is heavily pregnant, to be shown mercy and to be allowed to return to east London.
Speaking to The Times at a refugee camp in northern Syria, Ms Begum said she would “do anything required just to be able to come home and live quietly with my child”.
Her case has received high-profile backing, with a former MI6 chief saying the teenager should be given a chance “if we are to stand by our values”.
Meanwhile Anthony Loyd, The Times correspondent who found Ms Begum, said she was a “15-year-old schoolgirl who made a terrible mistake… and we must do our best to rehabilitate her amongst our own people”.
But her plea has been strongly rejected by others – including the brother of Alan Henning, the British aid worker beheaded by Jihadi John, who said she should “absolutely not” be allowed back.
Speaking to The Times, Mr Javid said: “We must remember that those who left Britain to join Daesh (IS) were full of hate for our country.
“My message is clear – if you have supported terrorist organisations abroad I will not hesitate to prevent your return. If you do manage to return you should be ready to be questioned, investigated and potentially prosecuted.”
Labour shadow home secretary Diane Abbott responded: “We are not in favour of making people stateless. However, if there are reasonable grounds to suspect that anyone who is entitled to return to this country either committed or facilitated acts of terrorism, they should be fully investigated and where appropriate prosecuted.
“Our priority must always be public safety. We need proper safeguards, particularly if the individual is associated with an international terrorist group. All significant risks must be thoroughly assessed.”
Any hopes of a rescue mission by British officials were swiftly quashed on Thursday as the Government ruled out an effort inside Syria to assist Ms Begum.
While refusing to comment on individual cases, Mr Wallace told the BBC: “I’m not putting at risk British people’s lives to go and look for terrorists or former terrorists in a failed state.
“There’s consular services elsewhere in the region and the strong message this Government has given for many years is that actions have consequences.”
While no official operation to remove Ms Begum from Syria will be carried out, questions have been raised over whether Britain would be able to prevent Ms Begum’s eventual return to the UK.
Former independent reviewer of terrorism legislation Lord Carlile told the BBC that if Ms Begum has not gained a second citizenship of another country, she will have to be allowed back to her homeland because under international law it is not possible for a person to be made “stateless”.
Meanwhile, Richard Barrett, a former director of global counter-terrorism at MI6, suggested it would be “unreasonable” to expect the Syrian Defence Force to look after her indefinitely.
He also warned that summary execution is the “most likely outcome” for such captured foreign nationals who are handed over to Syrian or Iraqi authorities.
Writing for The Guardian, he said: “Governments have a responsibility to address the problems created by their captured nationals and also to look more closely at why they made the choices they did.”
He added: “Even (Ms Begum), as unrepentant as she may be, should be given a chance, if we are to stand by our values – and if we believe our society is strong enough to reabsorb a 15-year-old who went badly off the rails.”
Ms Begum’s admission that she did not regret travelling to IS-controlled Syria, and her assertion that she is “not the same silly little 15-year-old schoolgirl who ran away from Bethnal Green four years ago” has been highlighted as a cause for concern by some.
Dr Kim Howells, a former counter-terrorism minister, told the Daily Mail: “She sounds to be completely unrepentant, she sounds cynical.”
Mr Henning’s brother Reg told The Sun: “The authorities should take her passport off her. She made her choice, didn’t she? She made her bed and she should lie in it.”
However, Ms Begum’s brother-in-law Mohammed Rehman told Mail Online that her family want her to be allowed to return and be “re-educated”.