The High Court in London has dismissed a British Government appeal against a ruling awarding British citizenship to Australian Guantanamo Bay detainee David Hicks.
Unlike Australia, Britain is opposed to the US military tribunals planned for the detainees at Guantanamo Bay and has successfully lobbied to have its citizens released from the camp.
Nine British citizens have been released from the Guantanamo Bay facility after requests from the Blair Government.
Hicks's relatives hope he will also be released.
The British Home Office can still appeal against the High Court's ruling.
In December the High Court ruled Hicks was entitled to a British passport because his mother was born in Britain.
The British Government appealed to the full bench of the High Court because of Hicks's alleged terrorist activities alongside the Taliban in Afghanistan.
Hicks has been detained at the US prison in Cuba for more than four years.
He is awaiting trial before a military commission on terrorism-related charges.
