An Algerian man suspected of terrorism involvement has been deported from Britain, the Home Office has said.
The home secretary says V is a threat to national security
The Algerian, the first to be deported to Algeria on national security grounds, had withdrawn an appeal against deportation, a spokesman said.
Three other Algerian terror suspects have reportedly also dropped appeals.
Britain is seeking to sign a "memorandum of understanding" with Algeria, aiming to guarantee anyone returned there will not be ill-treated.
But ministers are currently unable to forcibly deport terror suspects to Algeria because human rights laws say they cannot be returned to a country where they may face torture or ill-treatment.
A source close to the man, known as Mr V, said he had agreed to leave Britain out of "desperation" at his treatment by the government.
He added: "Imagine someone with a family being locked up in a high security prison, who does not know how long he is going to be held.
"This is a chance to be free in Algeria - but to build your life from scratch."
Mr V had been held at Long Lartin prison in Worcestershire.
He was accompanied by British officials, believed to be from the immigration service, on a scheduled flight from London to Algiers.
The Home Office spokesman said: "The British government is grateful to the Algerian authorities for their co-operation in facilitating the deportation of this individual.
"This is an indication of our shared commitment in the fight against terrorism and the warm relationship between our two countries."
The other Algerians who had dropped their appeals would be deported as soon as possible, he added.
"A number of others are appealing against deportation and their cases are currently before the Special Immigration Appeals Commission.
"Where a foreign national living in the UK poses a threat to this country, we will seek to remove them.
"Our priority is to protect public safety and national security, while upholding our international human rights obligations."
Director of human rights group Liberty, Shami Chakrabarti, said: "We all ought to be horrified that anyone in Britain has been made subject to such long-term mental anguish that he should choose to take his chances with torturers back home."