Britain's human rights watchdog called Saturday for an urgent independent probe into claims that the security services were complicit in the torture of more than 20 terror suspects.
The call came a day after a court heard that police were already investigating allegations that the services were complicit in the abuse of Britain's last remaining Guantanamo Bay detainee.
"Torture contravenes UK and international law and the values that Britain upholds," commission chair Trevor Phillips said.
"Ministers and government agencies are facing very serious allegations of knowing that UK citizens were being tortured, failing to take action to stop that torture and supplying questions to be used in the interrogation of men who were subjected to a high level of ill-treatment.
"Given the UK's role as a world leader on human rights, it would be inexplicable for the government not to urgently put in place an independent review process to assess the truth, or otherwise, of these allegations."
On Friday, the High Court heard that British detectives had applied for the release of secret documents related to their inquiries about Guantanamo inmate Shaker Aamer, held at the US detention camp on Cuba since February 2002.
"It became apparent they are now investigating allegations raised by Mr Aamer into the alleged complicity of the UK security service in his mistreatment," he said.
Aamer, 42, was born in Saudi Arabia but is a permanent British resident and is married to a British national who lives with their four children in London.
His lawyers told the court last year that government documents included evidence that British intelligence officers were present on at least two occasions when he was tortured but failed to help him.
Reacting to the Aamer case, the Foreign Office said it involved "a lot of unsubstantiated allegations."
"We do not accept allegations of UK involvement or 'complicity' in his mistreatment. We firmly reject any suggestion that we torture or mistreat people or ask others to do so on our behalf," said a spokesman.
He added: "We have made strenuous efforts on Shaker Aamer's behalf... We have maintained our requests for the release and return of Mr Aamer to the US government at the highest levels.
"This is a decision for the United States, and there is no guarantee that we will be successful."
Friday's court revelation came a week after a judge ordered the disclosure of torture evidence in the case of a former Guantanamo detainee, drawing criticism from US authorities.
In last week's case, involving British resident Binyam Mohamed, an Ethiopian national, the released documents showed that he had been shackled and told he would "disappear" if he failed to cooperate with US interrogators.
Since the ruling in the Mohamed case, British newspapers on both the right and the left have accused the government of seeking to cover up its involvement in the torture of terrorism suspects.
"The demand for a full and frank inquiry into the claims of complicity in detainee ill-treatment is fast becoming irresistible," Sean O'Neill wrote in the Times Saturday.
Foreign minister David Miliband has rejected the charges.
"There is no truth in the suggestion that we are complicit or cooperate in the outsourcing of inhuman treatment," he told the BBC.
Source: AFP European Edition