Britain is facing growing pressure to use its special relationship with the Obama administration to secure the freedom of the UK's last prisoner held at Guantánamo Bay.
The human rights group Amnesty International has written to the Foreign Secretary, William Hague, demanding "robust action" from the Government in the case of Shaker Aamer, a 43-year-old former British resident from London who has been held without charge or trial at the US detention centre for almost nine years.
In the letter, Amnesty's UK director, Kate Allen, tells Mr Hague that unless the UK intervenes in the case immediately, she fears Mr Aamer will languish in detention indefinitely.
Mr Aamer was among 16 former UK Guantanamo detainees to settle their compensation claims for complicity in torture against the Government. But his continued detention at the US Naval base raises questions about whether he is bound by the terms of the settlement, because he was not directly party to the negotiations.
Should he be released, he may continue his legal action in the UK. He claims that during his captivity in Afghanistan he was tortured in the presence of agents working for British secret services. These allegations are being investigated by Scotland Yard. On Wednesday, Mr Hague said he had told the US Secretary of State, Hillary Clinton, that the Government would like Mr Aamer returned to the UK, and that this being considered by the US.
Mr Aamer, held since autumn 2001, is originally from Saudi Arabia but is married to a British citizen and has four British children living in south London. He had permission to live indefinitely in the UK when he was originally detained in Afghanistan by Afghan forces.
Ms Allen said: "When it announced financial settlements for former Guantánamo detainees last week, the Government said it wanted to 'draw a line' under cases involving detention and alleged abuse overseas, yet Shaker Aamer is still languishing in a cell at Guantánamo. It was very welcome to hear a recent announcement by the Foreign Secretary that he has asked Secretary of State Clinton to return Shaker, but in the absence of charges or a proper trial we now need to see Mr Hague and the US authorities agreeing a specific timetable for Shaker's release."
Shaker Aamer's lawyer, Gareth Peirce, added: "How is it possible for our Government to talk of drawing a line under the past, when a British resident who has been hideously tortured over many years is still in unlawful detention? Are we really as a country prepared to allow his 10th year of captivity to begin in the hands of Britain's closest ally?"