A powerful committee of MPs and peers will this week begin an inquiry into hundreds of flights through UK airports which may be carrying terror suspects to destinations where they could face torture.

The United Nations and human rights lawyers have warned that the Government's failure to intercept the flights, some of which have been run by the CIA, could breach Britain's obligations under the UN Convention against Torture.

Tomorrow MPs and peers will begin questioning the use of "extraordinary rendition", where a suspect is snatched and taken to clandestine interrogation camps or to a country where torture may occur.

Yesterday the nine released British detainees from Guantanamo Bay were reunited for the first time and detailed the "acts of terror" inflicted on them by US authorities. The group spoke of the beatings, humiliation and isolation which became a way of life.

Among them was Moazzam Begg, who told international delegates: "We have been subjected to acts of terror. It's terrifying to have a gun with a loaded chamber pointed at your head; it's terrifying to think you will never see your family again; it's terrifying to feel a blade ripping your clothes off, all in the name of security. What does this tell us about the rule of law as far as the US is concerned? It tells us that it doesn't apply.''

Feroz Abassi said he was aware of one prisoner who had been beaten so badly he was put into a coma, and when he recovered from that was found to be permanently brain damaged, with a mental age of 12.

Leading human rights lawyers say that the Government's failure to take action makes them "complicit", and breaches the UN Convention against Torture, which Britain has signed.

Around 200 flights involved in the special operations are believed to have flown in and out of UK airports since September 2001. They include flights by the CIA's fleet of planes.

The Department of Transport said it had "no evidence" that the flights may be carrying people to destinations where they could be tortured. "These are privately chartered aircraft and they don't need to tell us who is on board," said a spokesman.

Philippe Sands QC, a leading human rights barrister, said: "You can't turn a blind eye under the torture convention. There is a positive obligation to investigate credible information."