There is evidence Britain was inappropriately involved in the rendition and ill-treatment of terror suspects, an inquiry has revealed.
Retired judge Sir Peter Gibson reviewed 20,000 top secret documents after allegations of wrongdoing by MI5 and MI6 officers in the wake of 9/11.
He found no evidence officers were directly involved in the torture or rendition of suspects.
But he said further investigation was needed into evidence of complicity.
Minister without portfolio Ken Clarke announced that a further investigation by a committee of MPs and peers will now be held into areas of concern highlighted by Sir Peter.
Sir Peter told reporters: "It does appear from the documents that the United Kingdom may have been inappropriately involved in some renditions. That is a very serious matter. And no doubt any future inquiry would want to look at that."
'Not robust enough'
In a statement to MPs, Mr Clarke said the guidance for intelligence agencies on detention and torture was "inadequate" in the immediate aftermath of 9/11 and "it is now clear that we were in some respects not prepared for the extreme demands suddenly placed on them".
The "oversight" of intelligence activities with detainees was "not robust enough," the former justice secretary added.
Mr Clarke did not rule out the possibility of a judicial inquiry into rendition claims after the Intelligence and Security Committee has completed its report.
Jack Straw, who was foreign secretary during the period covered by Sir Peter's report, welcomed the Parliamentary committee's investigation, at which he and other witnesses will be able to give evidence.
But he stressed that he never condoned the ill-treatment of terror suspects during his time in office.
"I was never in any way complicit in the unlawful rendition or detention of individuals by the United States or any other states," he told MPs.
He said he had agreed to the transfer of British nationals being held in the US to Guantanamo Bay but added: "We never agreed in any way to the mistreatment of those detainees or to the denial of their rights."
He urged MPs to accept "that we made repeated objections to the United States government about these matters and that I was able to secure the release of all British detainees from Guantanamo Bay by January 2005".
Sir Peter's report does not offer final conclusions because it did not have the chance to interview witnesses because of ongoing police investigations. Instead it sets out 27 issues he feels need to be examined further.
"It would be wrong to leave these issues, many of which relate to matters of policy, unexamined for the unknown amount of time it will take for the police to complete their related investigations," said Mr Clarke.
"The period of time was one in which we and our international partners were suddenly adapting to a completely new scale and type of threat from fundamentalist, religious extremists.
"Many UK intelligence officers had to operate in extraordinarily challenging environments subject to real personal danger. But everyone in the government and everyone in the agencies accept this bravery has to be combined with clear rules of proportionality, accountability, to ensure we uphold the values we are working hard to defend.
"While we accept intelligence operations must be conducted in the strictest secrecy, we also expect there to be strict oversight of those operations to ensure at all times they respect the human rights that are a cornerstone of this country's values."
Shadow justice secretary Sadiq Khan accused the government of going back on its 2010 promise to hold an independent "judge-led" inquiry into the allegations.
The Labour MP rejected Mr Clarke's claim that Sir Peter was unable to carry out a full inquiry, as originally planned, because it would interfere with ongoing police investigations.
He questioned whether the Intelligence and Security Committee, even with its recently beefed-up investigatory powers, was up to the task, given the need to "ensure any investigation is as independent and transparent as possible and has the full confidence of the public".