A prominent Libyan military commander is taking legal action against Jack Straw, the former British foreign secretary, to determine whether Straw signed papers allowing his rendition to Libya.
Abdel Hakim Belhadj, who became Tripoli's military commander after Muammar Gaddafi was toppled in last year's revolution, says the UK was involved in his illegal rendition to face imprisonment and torture in 2004.
A fellow former Gaddafi opponent, Sami al-Saadi, has also filed suit.
Lawyers for the two Libyan men said legal papers had been served on Straw following a report that he had approved the men's capture and transfer to Gaddafi's Libya while he was foreign secretary under Tony Blair's Labour government.
On April 15, the Sunday Times published an article, which quoted sources as alleging Straw had personally authorised the rendition to Libya of Belhadj and Saadi.
"The civil action is against Mr Straw personally and seeks his response to allegations that he was complicit in torture and misfeasance in public office," the Leigh Day & Co solicitors said in a statement.
"It seeks to examine his exact role in the rendition of Mr Al Saadi and Mr Belhadj as well as claiming damages from him personally for the trauma involved.
"However, Mr Belhadj has consistently made clear that his predominant aim in taking legal action is to seek an apology for what took place and for the truth to be known."
Straw told reporters he was unable to comment on the legal action because of the ongoing police investigation into the case.
UK ministers have denied any complicity in rendition or torture and Straw did not comment further.
Belhadj and Saadi are already suing the British government and Mark Allen, the former counter-terrorism director of spy agency MI6, after documents emerged suggesting his direct involvement in their rendition.
Files unearthed from Gaddafi's fallen regime last year said Belhadj was captured by the CIA in Bangkok in 2004 and with British help was forcibly returned to Libya, where he was jailed in the notorious Abu Salim prison.
Belhadj and his wife were living in exile in China in 2004 because of their involvement in the Libyan Islamic Fighting Group that fought against Gaddafi.
The couple was detained in the Malaysian capital, Kuala Lumpur, and were told they could travel to London despite not having EU passports and a UK visa, the paper had reported.
However, when the flight stopped in the Thai capital, Bangkok, the couple were detained in a secret CIA prison and eventually transferred to the Libyan capital Tripoli, according to the report.
Belhadj alleges that Straw was complicit in the "torture, inhuman and degrading treatment, batteries and assaults", saying the attacks were perpetrated on him by Thai and US agents, as well as Libyan authorities.
Saadi, meanwhile, says British agents helped detain him in Hong Kong in 2004 and return him to Libya, where he was subjected to years of torture.
The civil action being taken is against Straw personally, and Belhadj and Saadi's lawyers said they believed it was the first time legal action of this kind had been taken against a former foreign secretary.
Both men are seeking damages from Straw for the trauma involved.