Rendition apology demanded from MI6 and CIA by Libyan
The commander of anti-government forces in Tripoli says he wants an apology from Britain and America for his transfer to a prison in Libya in 2004.
Abdel Hakim Belhaj, then a terror suspect, says he was tortured after being arrested in Bangkok.
He says he was taken to Libya by a CIA and MI6 operation, allegedly confirmed by documents sent to Gaddafi's regime.
The Foreign Office said the government had a "long-standing policy" not to comment on intelligence matters.
Mr Belhaj told the BBC: "What happened to me and my family is illegal. It deserves an apology. And for what happened to me when I was captured and tortured.
"For all these illegal things, starting with the information given to Libyan security, the interrogation in Bangkok."
According to the Guardian, these documents were discovered in an abandoned office building in Tripoli by staff from Human Rights Watch.
Mr Belhaj said that MI6 and the CIA did not witness his torture at the hands of the former Libyan regime, but did interview him afterwards.
Letter of thanks
Sir Mark Allen, formerly MI6's director of counter-terrorism, has been reported to be the author of a letter to Moussa Koussa, thanking him for a "delicious" gift of dates and oranges, which was found among the recovered documents.
Mr Koussa served for years as Col Gaddafi's spy chief before becoming foreign minister. He defected in the early part of the rebellion, flying to the UK and then on to Qatar.
Rights groups have long accused him of involvement in atrocities, and had called on the UK to arrest him at the time.
BBC Middle East editor Jeremy Bowen, who has been shown the documents relating to Mr Belhaj, said the allegations were damaging "because we're talking about acts that were illegal".
Kim Howells, a former Foreign Office minister who became chairman of the Commons Intelligence and Security Committee, said his committee found no evidence of rendition by the UK.
But, he added, following the September 11 attacks, British intelligence would have been working closely with their Libyan counterparts.
"There were huge fears that Islamists - and the Libyan Islamic Fighting Group was an Islamist organisation - were going to try and do the same thing in London or Glasgow or Cardiff or whatever," he said.
"And I think there was an attempt by the security services and intelligence services to try and get hold of any information that might give a clue as to whether there were bombers at large."
Philippe Sands, a professor of international law, says he would not be surprised to find out that British security services and politicians were co-operating with Libyan officials in the fight against terrorism, but also said some questions needed to be asked.
"It's very troubling but consistent with a pattern of information and documents that's emerged in English court proceedings and elsewhere showing very close co-operation, shall we say.
"But this letter [referring to Abdul Hakim Belhaj] appears to be inconsistent with assurances given by most senior folk at MI5 and MI6 about who knew what when."
Other documents allegedly showing the CIA abducted several suspected militants from 2002 to 2004 and handed them to Tripoli were among thousands of pieces of correspondence from US and UK officials uncovered by reporters and activists in an office apparently used by Moussa Koussa.
The CIA would not comment on the specifics of the allegations.
The documents are also reported to suggest that MI6 also gave the Gaddafi regime details of dissidents.
These particular documents, found by Human Rights Watch workers, have not been seen by the BBC or independently verified. They allegedly reveal details about the UK's relationship with the Gaddafi regime.
One memo, dated 18 March 2004 and with the address "London SE1", congratulates Libya on the arrival of Mr Belhaj.
Meanwhile, China's government has admitted that Chinese arms manufacturers held talks as recently as July with representatives of Colonel Gaddafi's government who were seeking arms and ammunition as his forces battled rebels.
The meetings happened in China while a UN ban on such sales was in place. But China's Foreign Ministry has insisted that no actual weapons were supplied to Libya.