Shamima Begum, the woman who left Britain as a schoolgirl to join Islamic State, cannot effectively challenge the government’s decision to deprive her of British citizenship while she is in a detention camp in northern Syria, the court of appeal has been told. At the start of a two-day online hearing, her lawyers challenged a ruling by the Special Immigration Appeals Commission (Siac) this year that she has not been rendered stateless because she is entitled to Bangladeshi citizenship. Begum, now 20, was one of three east London schoolgirls who travelled to Syria to join Isis in February 2015. She lived under its rule for more than three years. In February last year she was discovered by journalists in a Syrian camp. She was nine months pregnant and said she wanted to return to the UK; shortly afterwards she gave birth. That month the then home secretary, Sajid Javid, informed her family that her British citizenship was being revoked. In March her baby son, Jarrah, died. After being moved to al-Roj, another camp in northern Syria, Begum initiated legal action remotely at the high court against the Home Office and against the decision of Siac, which hears challenges to decisions to remove British citizenship on national security grounds. Opening her case, Tom Hickman QC said the key issue was whether the absence of “a fair or effective means of challenging the decision to deprive her of her British citizenship” made the decision unlawful. He said the case breached “natural justice” as her appeal “cannot be pursued in a manner that satisfies even minimum requirements of fair procedure”. Hickman said Begum’s case was “the first case in which Siac has held that an appellant cannot have a fair and effective appeal”. The human rights organisation Liberty has intervened in her case to “uphold the right to a fair trial in the increasing use of ‘citizenship stripping’ by the Home Office”. In a statement released outside the court, Katie Lines, a lawyer with Liberty, said: “Banishing someone is not the act of a responsible government … [It] has other powers at its disposal, including criminal law, which it can and should use to deal with those suspected of terrorism. “Due process and the right to a fair trial is not a privilege to be handed out when the government sees fit. Ensuring we are all equal before the law is a principle that protects all of us.” Sir James Eadie QC, representing the Home Office, said in written submissions: “The fact that the appellant could not fully engage with the statutory appeal procedure was a result of her decision to leave the UK, travel to Syria against Foreign and Commonwealth Office advice and align with [Isis]. “This led to her being held in conditions akin to detention in a foreign state at the hands of a third party, the Syrian Defence Force. It was not the result of any action by the [home secretary].” Eadie added that Begum had been able to speak to her lawyers, and argued that “the fact that it might not be possible to mirror the level of access to legal advice that would be available if someone were at liberty in the UK does not mean the proceedings are unfair”. The hearing continues. The judges are expected to reserve their decision to a later date.