The British government promised a judge on Wednesday it would consider this week whether to ask Washington to free an Australian prisoner in Guantanamo Bay who won the right to claim British citizenship.
David Hicks, an Australian convert to Islam who was captured in Afghanistan, won the right to claim citizenship in the High Court in December because his mother was born in Britain.
Britain has already secured the release of all nine British citizens who were held at the U.S. prison camp in Cuba. It says it does not believe U.S. plans for military trials of detainees would be fair.
But Hicks's native Australia, which has been more supportive of the United States over Guantanamo, has refused to ask Washington to free him.
His lawyers sought British citizenship for him in the hope they could force London to intercede on his behalf. The High Court has ruled that he should receive whatever assistance the government would give to any other British citizen, but so far London has yet to take any action.
Hicks's lawyers took the government to court on Wednesday, arguing that the Foreign Office had been too slow to act.
A Foreign Office spokesman said the government's lawyer had told Judge Andrew Collins that Foreign Secretary Margaret Beckett would be presented with the case this week to consider what help, if any, to give Hicks.