A Libyan politician and his wife are appealing today against a High Court decision to throw out damages actions brought over their rendition to Tripoli.
In December, Mr Justice Simon said the claims of Abdul Hakim Belhaj and Moroccan Fatima Boudchar against former foreign secretary Jack Straw and Sir Mark Allen, ex-head of counter-terrorism at MI6, should be struck out on the basis that they were non-justiciable.
The couple want compensation and declarations of illegality arising out of the UK's alleged participation in their abduction, detention and rendition in March 2004 and their alleged mistreatment.
Mr Belhaj, a leading figure in the rebel forces before Colonel Muammar Gaddafi was killed, claims that British intelligence was responsible for providing information that facilitated their rendition.
The case covers a period from when the couple were detained by Chinese authorities at Beijing airport for two days before being deported to Malaysia and held for two weeks before being flown to Thailand, ostensibly en route to London, and later taken to Libya on an aircraft said to be owned by a CIA front company.
Mr Belhaj says that, in Bangkok, they were detained by American intelligence and he was tortured while his pregnant wife was chained to a wall. When they got to Tripoli, he spent six years in jail and his wife was released shortly before giving birth.
Rory Phillips QC told the judge that the alleged unlawful detention and mistreatment was carried out by officers of the states concerned - none of whom were defendants in the action - and not the UK authorities.
The Government was said to be liable on the principles of secondary liability by acquiescing, assisting, encouraging and conspiring in what happened.
There was no allegation against any UK official or that any detention or mistreatment took place in the UK or in UK-controlled territory, and it was not claimed that either claimant had any connection with the UK.
The judge said he had concluded with hesitation that the defendants were correct in their submission that the case put forward against them depended on the court having to decide that the conduct of US officials acting outside the United States was unlawful, in circumstances where there were no clear and incontrovertible standards for doing so and where there was incontestable evidence that such an enquiry would be damaging to the national interest.
The hearing at the Court of Appeal is before the Master of the Rolls Lord Dyson, Lord Justice Lloyd Jones and Lady Justice Sharp.