Successive British governments have always said they were never complicit in illegal rendition and torture but that may not be the case.
The BBC has obtained documents that suggest that MI6 was involved in the rendition of Abdel Hakim Belhaj who was believed to be helping recruit British jihadis for Iraq.
The BBC also now understands that the British government authorized MI6's intervention in tipping off its foreign intelligence partners as to the whereabouts of Mr Belhaj which subsequently led to his rendition, imprisonment and alleged torture in Libya.
Peter Taylor explained that in 2004, Mr Belhaj was then the leader of the Libyan Islamic Fighting Group and MI5 believed it was close to Al Qaeda and was involved in recruiting young Muslims in Britain to fight Jihad in Iraq.
On the involvement of MI6, he said that Sir Mark Allen, a very senior MI6 officer, discovered that Mr Belhaj was in Malaysia and about to head for London in the hope of obtaining political asylum.
Sir Mark informed his foreign intelligence partners and as a result he was intercepted in Bangkok, presumably by the CIA, and rendered to Libya where Mr Belhaj says he was imprisoned and allegedly tortured.
Peter said that it only came to light as a result of an accident in which a letter from "M", who is believed to be Sir Mark, to the Head of Libyan intelligence, Musa Kusa, was found in the rubble of Musa Kusa's Headquarters.
In the letter Sir Mark refers to Mr Belhaj as "air cargo" and congratulates Musa Kusa on its "safe arrival" and points out that "the intelligence was British".
Jack Straw, who was foreign secretary at the time has only commented once saying that his government was opposed to unlawful rendition and torture and were not complicit and nor did they turn a blind eye.
But he added that no Foreign Secretary can know all the details of what its intelligence agencies are doing at any one time.
Watch Modern Spies on BBC 2 at 21:00 BST on Monday 9 April for more on this story.
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