An allegation that officers from Secret Intelligence Service MI6 were complicit in torture is to be investigated by the Metropolitan Police, it was revealed today.
Scotland Yard said the Attorney General, Baronness Scotland, asked it to investigate "the conditions under which a non-Briton was held" and the "potential involvement of British personnel".
The case is unrelated to that of Binyam Mohammed, which Metropolitan Police officers are also investigating, a spokesman said.
A Metropolitan Police spokesman said: "We can confirm that the Attorney General asked the Metropolitan Police to investigate a case that was a referral from the Secret Intelligence Service.
"This is unrelated to Binyam Mohamed but looks at the conditions under which a non-British citizen was detained and the potential involvement of British personnel.
"An investigation is ongoing."
Foreign Secretary David Miliband confirmed the investigation in a letter to his Tory counterpart.
He said the case was referred by MI6 "on its own initiative" and was not prompted by an accusation against SIS or the person concerned.
He said: "As you are aware, the police are already looking at allegations related to Mr Binyam Mohamed.
"One further case has subsequently been referred by the Attorney General to the police.
"This case was referred to the Attorney General by SIS on its own initiative, unprompted by any accusation against the Service or the individual concerned.
"It is for the police to investigate. The Government cannot comment further both to avoid prejudice and to protect the individuals involved.
"The scope and handling of any police investigation is a matter for the police themselves."
The Metropolitan Police said it would not discuss the case further.
Details of the specific allegations, the place and date on which they are alleged to have occurred, who they were made against and by whom is unclear.
Mr Miliband said the UK Government had a "principled stance" against torture.
He said Britain's security and intelligence services were "the best in the world" and praised their "integrity and bravery".
He said: "The Government wholeheartedly condemns torture. We will not condone it. Neither will we ever ask others to do it on our behalf.
"This is not mere rhetoric but a principled stance consistent with our unequivocal commitment to human rights.
"We are fortunate to have the best security and intelligence services and armed forces in the world. We are all safer because of the work they do with integrity and bravery."
Scotland Yard is already looking at claims made against MI6's sister organisation, MI5, by Mohamed, a former resident of Guantanamo Bay.
He says officers from the Security Service, which is tasked with countering threats against UK national security, were complicit in his torture while he was held in Pakistan, Morocco and Afghanistan.
Only last month Sir John Scarlett, the head of MI6 said there was "no torture and no complicity in torture" by SIS agents.
He told a BBC documentary: "Our officers are as committed to the values and the human rights values of liberal democracy as anybody else.
"(They) have the responsibility of protecting the country against terrorism and these issues need to be debated and understood in that context."
He also stressed that British intelligence services had not been compromised by close relationships with similar services in the US.
"Our American allies know that we are our own service, that we are here to work for the British interests and the United Kingdom," Sir John said.
"We're an independent service working to our own laws - nobody else's - and to our own values."
