The UK has signed an agreement with Libya saying that foreign nationals deported there will not be mistreated.
Colonel Gaddafi: Deal over torture
Under international convention the UK does not send people back to countries where they may face inhuman or degrading treatment.
The UK government has been seeking assurances from several countries that no-one it deports will be ill-treated.
Ministers say the moves are important in fighting terrorism, but civil liberty groups condemned the deal.
The memorandum of understanding (MOU) between the UK and Libya was signed in Tripoli by Britain's Ambassador to Libya, Anthony Layden, and the Libyan Acting Secretary for European Affairs, Abdulati Ibrahim al-Obidi.
A similar agreement was signed with Jordan earlier this year.
Home Secretary Charles Clarke said the agreement was necessary to help combat terrorism.
"I believe these, and the other ongoing negotiations, are an example of the effective international cooperation that we need in order to confront and defeat the type of terrorism we now face," he said.
"As we confront the terrorist threat facing Britain today we have to ensure that the right of people to travel around freely is balanced with our international obligations to protect the rights of individuals facing torture."
Shadow home secretary David Davis welcomed the agreement.
"It is important now that the government doesn't drag its heels in rounding up and deporting extremists. Preachers of hate who have no right to be here should be swiftly removed," he said.
The government is hoping to reach similar agreements with Lebanon and Algeria, the prime minister's official spokesman said later.
It is understood that about four or five Libyans could be deported following the agreement.
Commenting on the UK's agreement with Libya, Shami Chakrabarti, director of civil rights group Liberty, said: "It would no doubt be very good news if Colonel Gaddafi could now be trusted not to indulge in torture.
"However, fundamental rights are too precious to gamble with. The 2004 Foreign Office Human Rights report expressed 'serious concerns' as to the conditions in Libyan prisons."
Kate Allen, Amnesty International's UK director, said it was "dangerously misguided to expect countries with a known record of torturing people to respect bits of paper promising not to torture".
Mark Oaten, Liberal Democrat home affairs spokesman, said: "If Amnesty has concerns about torture then they will know better than a minister in Whitehall what is really going on, and we should listen to their concerns."