Shamima Begum, the British schoolgirl who left the UK with her friends aged 15 to join ISIS, is appealing for the return of her citizenship.
Ms Begum, now 20, was stripped of her citizenship by former home secretary Sajid Javid in February last year and is now back at the High Court in a second attempt to have it restored.
She left her home in London with two other schoolgirls in 2015 and travelled to Syria. Within three weeks she had married Dutch ISIS fighter Yago Riedijk and then had three children, all of whom have died.
Ms Begum was discovered in a refugee camp in Syria in 2018.
Last year she took legal action against the Home Office at the High Court and the Special Immigration Appeals Commission, a specialist tribunal that deals with decisions to remove someone's British citizenship on national security grounds.
On Thursday, the High Court heard Ms Begum has no hope of a "fair and effective appeal" because she is not allowed in the country.
Tom Hickman QC called for the decision to be revoked and said depriving her of the right to defend herself in the UK was a "breach of natural justice".
"The consequence of the appellant not being able to have a fair and effective appeal means that the secretary of state's decision stands indefinitely and possibly forever without there ever having been a judicial decision on the [appeal's] merits. That, we say, piles unfairness upon unfairness and is wrong in law," he said.
Sir James Eadie QC, representing the Home Office, said that Ms Begum's inability to "fully engage with the statutory appeal procedure" was a result of her decision to travel to Syria.
“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," he said.
“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].”
Her lawyers have previously argued that the decision to remove her citizenship was unlawful because it left her stateless but the government's case is that she was a "citizen of Bangladesh by descent" at the time.
Her family have previously argued that she has never had a Bangladeshi passport and that she was from the UK.
The two-day hearing will continue on Friday and the court is due to reserve its judgment to a later date.