The home secretary has warned he “will not hesitate” to block the return of a British teenager who left the UK to join Isis.
He added that if the heavily-pregnant Ms Begum did return to Britain, she could be prosecuted, despite protestations from her family, who argue she was just a child when she fled to Syria aged 15.
“My message is clear – if you have supported terrorist organisations abroad I will not hesitate to prevent your return,” Mr Javid told The Times.
“If you do manage to return you should be ready to be questioned, investigated and potentially prosecuted.”
The home secretary’s comments came after security minister Ben Wallace said he would not authorise a rescue operation to facilitate Ms Begum’s return to the UK.
The teenager is currently living in Syrian camp, where she is being held alongside around 40,000 other family members of Isis fighters.
“I’m not putting at risk British people’s lives to go and look for terrorists or former terrorists in a failed state … actions have consequences,” Mr Wallace told the BBC.
“Some were groomed when they were young but are now adults – some of them are hardened fighters.”
While an official mission to retrieve Ms Begum from Syria looks unlikely to take place, questions have been raised over Mr Javid’s assertion she could be prevented from returning to the UK altogether.
The former independent reviewer of terrorism legislation, Lord Carlile, told the BBC that if Ms Begum did not have a second nationality she would have to be allowed to return to her homeland under international law preventing a person being 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.
Ms Begum was one of three schoolgirls, along with Kadiza Sultana and Amira Abase, from Bethnal Green Academy in east London who left the UK in February 2015.
Another girl, Sharmeena Begum, also from Bethnal Green but not related to Shamima, had travelled to Syria two months earlier.
Ms Sultana was reported to have been killed in an airstrike in 2016, while Shamima Begum has said she recently heard second-hand the other two women may still be alive.
Debate has raged over whether the group, who were all either 14 or 15 at the time they left the UK, should be considered responsible for their actions or the victims of Isis “brainwashing”.
Hussen Abase, father of Amira Abase, has called for the women to be allowed to return home, insisting they had “made a mistake”.
“Before teenagers do anything, they don’t contemplate [what will happen],” he said: “They can be easily tricked … their age makes them vulnerable.”
Ms Begum, who recently fled the remaining pocket of Isis-held territory, said two of her children had died while she was in Syria and she wanted to return to the UK to ensure the safety of her third child.
However, she has showed little remorse for her actions and appears indifferent to the group’s brutality, recalling she was “unfazed” by seeing a severed head in a bin.
“I don’t regret coming here,” she told The Times. “I’m not the same silly little 15-year-old schoolgirl who ran away from Bethnal Green four years ago.”
More than 400 British Isis fighters are already thought to have returned to the UK, with a report in 2017 warning many have since fallen off the radar of security services.
The government estimates roughly 900 people “of national security concern” travelled from Britain to Iraq or Syria to engage in the conflict, 40 per cent of whom have now returned, while a further 20 per cent have been killed.
Additional reporting by PA
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