The two men are now launching a civil action against Sir Mark Allen, claiming that evidence of the UK’s role in the couple’s rendition is detailed in a number of documents held by the Libyan security services, which came to light after the fall of Colonel Muammar Gaddafi’s regime.
One of those cases to be investigated involves the former rebel who now commands military forces in Libya, Abdel-Hakim Belhaj, and his wife Fatima Bouchar.
Mr Belhaj, who led the storming of Muammar Gaddafi’s Bab al-Aziziya compound last August, claims that after attempting to seek asylum in the UK in 2004, the couple were detained at the airport and deported to Kuala Lumpur, where he was held for several weeks.
He further claims that he was rendered to Libya by the US authorities via Bangkok, and was imprisoned for six years in some of the country’s worst jails, including Abu Salim in Tripoli.
Mr Belhaj claims that whilst imprisoned, he was interrogated by British agents.
Last October, classified documents were discovered in Tripoli that revealed MI6 played a significant role in the rendition of Mr al-Saadi (also known as Abu Munthir).
It has been reported that a fax the CIA sent to the then Libyan Foreign Minister Moussa Koussa “shows that the agency was eager to join in the Saadi rendition operation after learning that MI6 and Gaddafi’s government were about to embark upon it”.
Sapna Malik, who is representing the men and their families, said: “We are taking this unusual step of preparing a legal action against an individual as the documents we have in our possession suggest Sir Mark was directly involved in the unlawful rendition of our clients and their families.
“The documents, which have so far come to light, raise serious questions to answer, particularly in light of the horrendous treatment to which our clients were subjected.
“There must be full accountability for this dark episode.”
Sir Mark, who was the director of counter-terrorism at MI6 until he left in 2004, has been notified of the intended legal proceedings against him, the pair’s lawyers at Leigh Day & Co said.