People trafficked to Syria and “brainwashed” can still be threats to national security, the Home Office has said in Shamima Begum’s appeal against the stripping of her British citizenship.

Ms Begum was 15 when she travelled from Bethnal Green, east London, through Turkey and into territory controlled by the so-called Islamic State (IS).

Her British citizenship was revoked on national security grounds shortly after she was found, nine months pregnant, in a Syrian refugee camp in February 2019.

Ms Begum, now 23, is challenging the Home Office at the Special Immigration Appeals Tribunal (SIAC) over the decision to remove her British citizenship.

If you have been exposed for prolonged periods there is an almighty problem

SIAC has heard that, according to the security services, people who travelled to Syria to align with IS “were likely to have been radicalised, to have contributed to the continuance of Isil as an entity and may have received military training, fought with Isil or taken part in terrorist attacks”.

“They were exposed to routine acts of extreme violence, which would be likely to have had the effect of desensitising individuals and encouraging them to view violent terrorist activity as an ‘acceptable and legitimate course of action’,” the court was told in written submissions.

On Thursday, Sir James Eadie KC, for the Home Office, said Ms Begum was exposed to four years in IS-controlled territory prior to the removal of her British citizenship in 2019.

He later referenced statements Ms Begum made to the media, including in an interview where she said she was not “fazed” about seeing a head in a bin.

“If you have been exposed for prolonged periods there is an almighty problem,” Sir James said.

The barrister also said the security services have identified several potential risks from people who have returned to the UK from IS-controlled territory, including being involved in the planning or execution of terror attacks.

You can be trafficked in the most ghastly, unacceptable way, exposed in the most unacceptable way, desensitised in the most unacceptable way and yet unfortunately... still be a security threat

“Simply providing support, couriering, providing funds and logistical support… They do not have to be bombers themselves,” Sir James added.

Ms Begum’s lawyers said she was “recruited, transported, transferred, harboured and received in Syria for the purposes of ‘sexual exploitation’ and ‘marriage’ to an adult male”.

But Sir James said on Thursday the threat posed to national security is the most important factor.

“You can be trafficked in the most ghastly, unacceptable way, exposed in the most unacceptable way, desensitised in the most unacceptable way and yet unfortunately… still be a security threat.”

He said: “If they do pose such a danger, how they came to pose that danger is not important. What matters is that they do in fact pose such a danger.”

He added: “No one disputes that it is entirely possible for a person to have been trafficked or manipulated or brainwashed or similar and yet be the most serious danger to the public.

“A threat to national security means someone who poses a threat to the public.”

Sir James previously said then-home secretary Sajid Javid was aware of Ms Begum’s “age and circumstances of her travel to Syria” when he made the decision to deprive her of her British citizenship.

What evidence is available shows that rather than viewing the appellant as a victim, a child that was manipulated and exploited, the Home Secretary proceeded on the basis that she acted 'voluntarily' in travelling to Syria and aligning with Isis

The barrister later said Ms Begum travelled to Syria “with her eyes open” about the brutality of IS.

He said: “She travelled for the purpose of aligning with Isil and once in Syria she did align with Isil.

“The assessment is that she did that with her eyes open. The ideology of Isil and their uncompromising brutality had been widely covered in the media.”

Ms Begum’s lawyers argued she was “persuaded, influenced and affected with her friends by a determined and effective Isis propaganda machine”.

Samantha Knights KC continued in written submissions: “What evidence is available shows that rather than viewing the appellant as a victim, a child that was manipulated and exploited, the Home Secretary proceeded on the basis that she acted ‘voluntarily’ in travelling to Syria and aligning with Isis.”

Thursday marked the end of the public proceedings, with Friday’s hearing expected to be held in private.

Mr Justice Jay said: “The commission will be reserving its judgment in this case, there will be a closed judgment and an open judgment.”

The judge then said he was concerned about the potential of the judgment being leaked between it being sent to the lawyers on both sides and the ruling being made public.

“It may be inhumane to Ms Begum or may give her false hope depending upon the result,” the judge said.

The ruling is expected to be given in writing next year.