Gordon Brown is facing increasing pressure to directly intervene in the case of a British resident being held at Guantanamo Bay who has been charged with terrorism-related offences and may face the death penalty.
MPs, human rights lawyers and former Guantanamo inmates have called on the Prime Minister to help secure the release of a 29-year-old Londoner, Binyam Mohamed, who has been held by the Americans for more than six years without trial.
Mr Mohamed claims to have suffered horrific abuse at the hands of his American captors, including razor blade cuts to his genitals. He has been formally charged with terrorism-related offences and is now due to be brought before a US Military Commission.
The Liberal Democrat MP Sarah Teather, chair of the all-party parliamentary group on Guantanamo Bay, said: "The American government have disgracefully undermined their own case by allowing Binyam Mohamed to be subjected to such horrendous abuse.
"If Binyam Mohamed has committed a crime, then it is right that he is charged and brought to justice. However, any trial process must be fair, open and transparent. Holding people for years on end without charge or trial breaches every single value that the war on terror purports to defend."
Her words echoed those of the Liberal Democrat foreign affairs spokesman Ed Davey. Speaking before news of the charge broke, he said: "This detainee has now served over six years in prison without charge or trial. The British Government must insist that this individual gets his long overdue day in court. It is essential that democratic countries stand up for fair trials and due process, whether at home or abroad."
Louise Christian, the human rights lawyer who represented three British citizens formerly imprisoned in Guantanamo Bay, urged the Government to do everything in its power to bring Mr Mohamed home. "Britain has more of a duty to rescue someone who is about to go before an unfair trial. If we don't, then it will lead to a shameful spectacle being played out before the world."
Moazzam Begg, who was released from Guantanamo Bay in 2005, said the case of Mr Mohamed was paradoxical to his own. "I was released because I was due to go before one of these Military Commissions. Binyam is being held because he is expected to be charged and brought before the very same commission."
Mr Mohamed, born in Ethiopia in 1978, came to Britain as an asylum-seeker in 1994 when he was 16. According to his legal team, he went travelling to Pakistan and Afghanistan in 2001 in an attempt to deal with his health and personal problems. He was arrested in Pakistan in April 2002.
His lawyer, Clive Stafford Smith, director of the human rights group Reprieve, said his client was innocent of any allegations relating to terrorism. But he added: "We do not ask anyone merely to accept Mr Mohamed's claims, but we do ask that he be given an open trial in which to present to a fair jury and that he be allowed access to the evidence with which to prove his case."
Mr Mohamed's legal team has instructed lawyers to challenge the British Government in court over its alleged retention of evidence that would prove Mr Mohamed had been tortured and rendered to Morocco.