Britain signed a deportation agreement with Libya on Tuesday guaranteeing that foreign nationals returned there will not be mistreated.
British Prime Minister Tony Blair's government is bolstering its powers to expel radical Islamic preachers and terror suspects from Britain. A similar agreement was signed with Jordan in August.
As a signatory to the European Convention on Human Rights, Britain is not allowed to deport people to countries where they may face torture or mistreatment. It is seeking similar agreements with eight other countries, including Algeria, Lebanon and Tunisia.
Civil rights campaigners and the UN special envoy on torture, Manfred Nowak, have warned, however, that such assurances have no weight in international law and would not sufficiently protect the deportees.
Home Secretary Charles Clarke said the agreement was necessary to help Britain combat the threat of terrorism.
"I believe these, and the other ongoing negotiations, are an example of the effective international co-operation that we need in order to confront and defeat the type of terrorism we now face," he said.
The agreement was signed in Tripoli by Britain's Ambassador Anthony Layden and Ibrahim al-Obidi, Libya's acting secretary for European affairs.