British Prime Minister David Cameron has set up a panel to look into allegations that British security services were involved in delivering terrorism suspects to Libya, knowing that they would be tortured.
In a speech to Parliament on Monday, Cameron said the investigation will examine whether "relations between the British and Libyan security services became too close."
Human Rights Watch said it found documents that appear to incriminate Britain's intelligence services in planning the 2004 capture and rendition of Abdel-Hakim Belhaj.
Known at the time as Abu Abd Allah Sadiq, Belhaj is the current military chief of Libya's rebel-led provisional government.
Belhaj has said he was tortured by the CIA before being transferred to Libya. He says he was tortured again by the Libyan government, then interviewed by British agents.
Belhaj at the time was suspected of having ties to al-Qaida.
The human rights organization found the memos in papers abandoned in the Tripoli offices of Libya's former spy chief, Moussa Koussa.
Koussa fled to London and then Qatar from Libya earlier this year.
The inquiry, led by former appeal court judge Peter Gibson, was set up by Cameron to investigate claims that Britain's former government knew about the torture of terrorism suspects in foreign countries.
Britain's Foreign Office has declined to comment.
Some information for this report was provided by AP, AFP and Reuters.