A Libyan military commander is taking legal action against Jack Straw following allegations the former foreign secretary personally permitted his illegal rendition.
Lawyers representing Abdel Hakim Belhadj confirmed legal papers had been served on the Labour MP after reports suggested he had signed documents that allowed the rebel to be sent back to his homeland in 2004.
Mr Belhadj, 45, claims he had been living in exile in Beijing, China, before being detained with his wife Fatima while en route to the UK where they were trying to seek asylum. He alleges they were sent back to Libya - which was under the rule of Muammar Gaddafi - and imprisoned and tortured.
The civil action, which is against Mr Straw personally, seeks to examine his exact role in the rendition and claim damages from him for the trauma involved.
Mr Belhadj's lawyers Leigh Day & Co said they sent the MP a letter on Tuesday asking him to produce a number of documents. They include papers mentioned in a Sunday Times article which alleged that Mr Straw signed off the rendition, as well as his diaries, memoirs and notes from March 2004 onwards.
Sami Al Saadi, who claims to have shared the same fate as fellow Libyan and Gaddafi opponent Mr Belhadj, is also taking legal action against Mr Straw.
Mr Belhadj, a key military figure in the uprising that toppled Gaddafi last year, is already suing the Foreign Office and MI6. He alleges that he was tortured by Gaddafi's regime after being rendered back to Libya via British-controlled Diego Garcia in 2004.
The Metropolitan Police are already investigating the claims. British ministers have always denied any complicity in rendition or torture.
The Sunday Times reported at the weekend that Mr Straw had been confronted about his alleged role by MI6.
Sapna Malik, a partner at Leigh Day & Co, said: "We have said all along that liability must follow the chain of command. These latest revelations bring us closer to that goal. If the former foreign secretary does not now own up to his role in this extraordinary affair, he will need to face the prospect of trying to defend his position in court."