Shamima Begum’s lawyers argued before the court of appeal on Tuesday that it was unlawful to deprive her of British citizenship because she was a victim of trafficking when she left the UK for Islamic State territory in Syria at 15. Samantha Knights KC, her barrister, told the start of a three-day hearing that the Home Office and a lower court had failed to properly consider whether she was groomed – and called for the decision to be overturned. Knights accused Sajid Javid, the then home secretary who removed her citizenship, of having failed to consider whether Begum, then a schoolgirl in east London, was groomed and trafficked and so breached anti-slavery protections in British law. “The appellant’s trafficking was a mandatory, relevant consideration in determining whether it was conducive to the public good and proportionate to deprive her of citizenship, but it was not considered by the Home Office,” Knights said in a written submission. “As a consequence, the deprivation decision was unlawful.” An initial decision upholding Javid’s ruling by the special immigration appeals commission (Siac) made in February this year, should also be overturned by the appeal court on similar grounds, Knights added. Although the Siac court had acknowledged there was credible suspicion that Begum “was recruited, transferred and then harboured for the purpose of sexual exploitation”, that was “insufficient” for the commission to deem the home secretary’s decision unlawful, in its ruling. The Home Office, which is due to begin its evidence on Wednesday, is opposing the claim on national security grounds. It argues that the fact that a person may have been manipulated does not mean they cannot be a terrorist risk. The hearing, before three senior judges, is the latest step in a long-running legal battle that dates back to Javid’s decision to remove Begum’s British citizenship in 2019, after she was picked up by Syrian Kurdish forces after the defeat of Islamic State. Begum had left her home in Bethnal Green, east London, in 2015 with two school friends, and travelled to Syria to live under Islamic State rule. When interviewed immediately after the terror group’s defeat she said: “I don’t regret coming here.” That prompted Javid to remove her British citizenship, arguing it was “conducive to the public good” and that she would not be rendered stateless, because she could claim Bangladeshi citizenship through her parents, even though she had never been to the country and it had said it did not want her. Begum remains in Kurdish custody in north-east Syria, and she has said more recently she regrets her decision – arguing she would “rather die than go back to IS” – and that she would be willing to face terror charges in a British court if necessary. The case has already been before the supreme court once, which largely ruled against Begum, but gave her a chance of launching a fresh legal action if she was able to properly instruct solicitors – leading to the latest round of cases. Knights’ written submission to the appeal court argues that Begum had been “groomed over the previous months” before leaving the UK in February 2015 and that her travel had been “facilitated by a man who worked for Isil [Islamic State]” who “was also an agent for the Canadian Security Intelligence Service”. Begum was met at Istanbul bus station for the onward journey to Syria by a man called Mohammed al-Rashed, who British police have acknowledged also acted as an informant for Canada’s CSIS spy agency. Her lawyers also blamed “state failures” that allowed her to leave the UK, with the Met police, her school and Tower Hamlets council all in effect contributing to Begum’s trafficking through their shortcomings. “The state failures in the present case were highly pertinent bearing in mind what steps could readily have been taken by state bodies to protect the appellant and prevent her leaving the UK, and how swiftly the appellant’s family acted when they were alerted to her having gone missing,” Knights told the court. Written submissions from Sir James Eadie KC, for the Home Office, argue that the law allowed Javid discretion in which factors to take into account before deciding to revoke a person’s British citizenship. “The secretary of state was well aware of the possibility that she may have been ‘manipulated or radicalised’ prior to her travel,” Eadie said. “The only question which therefore remained was what weight to attribute to these factors. That was a matter for the secretary of state.” The advice of the British security service MI5 to Javid, as disclosed in previous court hearings, was that Begum had remained in Islamic State territory for four years, until she was 19, and that she had aligned with the terror group. “Public sentiment [in the UK] is overwhelmingly hostile [to her],” the agency added. Oral arguments in the court of appeal are expected to conclude on Thursday, with a decision expected at a later date. The presiding judges are Lady Chief Justice Lady Carr, Lord Justice Bean and Lady Justice Whipple.