Amnesty International UK has criticised the British government's use of diplomatic assurances to deport alleged terror suspects to countries where they face torture or death.
The human rights group says such assurances, or memorandums of understanding, are "unenforceable" and "unreliable", and that the UK should comply with international standards in such cases.
In a new report, Amnesty accuses the government of being "the most influential and aggressive" employer in Europe of "no-torture deals" to forcibly deport people to countries like Libya, Jordan, Algeria and Russia.
The NGO, which criticises other European governments too, says: "The UK government has been the most influential and aggressive promoter in Europe of the use of diplomatic assurances to forcibly return people it considers threats to national security to countries where they would face a real risk of serious human rights violations, including torture or other ill-treatment."
Amnesty criticises the Foreign Office for negotiating these memorandums with countries including Jordan, Lebanon, Libya and Ethiopia.
Amnesty says that, "as the research and opinion in this report demonstrates, governments are using diplomatic assurances in their own self-interest to rid themselves of foreigners alleged to be involved in acts of terrorism instead of prosecuting those persons for any crimes of which they are accused."
Under international law, the ban on torture and other ill-treatment, including sending a person to a place where he or she is at risk of such abuse, is absolute.
Through relying on such deals the UK and other countries are in breach of the UN convention against torture, Amnesty points out.