The family of a Brighton law student detained at Guantanamo Bay are due to find out if the British government will be forced to help him.
Omar Deghayes fled to the UK from Libya in the 1980s
Omar Deghayes, 36, has been imprisoned at the US military base in Cuba since his arrest in Pakistan in 2002.
He is accused of committing terrorist acts against the United States.
Ministers refused to get involved as Mr Deghayes is not a British citizen. The High Court will decide whether or not to order a judicial review on Friday.
The judges will decide if ministers should think again.
Mr Deghayes has been held without charge at Guantanamo Bay and has recently gone on hunger strike.
But the Foreign Office has said the government does not have legal responsibility for a non-British subject.
Mr Deghayes, who was born in Libya and was educated in the UK, had applied for British citizenship.
He was granted refugee status in the UK after fleeing Libya with his family in the 1980s when his father was assassinated.
The American authorities claim Mr Deghayes is a Chechen rebel and say they have video footage of him brandishing a Kalashnikov.
But the detainee's lawyer, Clive Stafford-Smith, said it was a case of mistaken identity.