Five British residents are among more than 300 detainees
Four of the five British residents held by the US at Guantanamo Bay are to be released, the BBC has learned.
The UK government requested the release of all five men in August after previously refusing to intervene as they were not British citizens.
Jamil el-Banna, Omar Deghayes and Abdenour Samuer will come back to the UK, while Shaker Abdur-Raheem Aamer will return to his native Saudi Arabia.
The government has not confirmed the move and a release date is unknown.
The men's lawyer, Clive Stafford Smith, said: "There's no doubt that the agreement has been struck, that they will return home. The question is, when?
"There's no reason why they couldn't come home tomorrow, but the US are insisting on a lot of red tape."
He said it was possible that British police could question them on their return to the UK, but doubted they would be detained further "because they are not a threat to Britain in any way".
The fifth British resident held at Guantanamo, Ethiopian Binyam Mohammed al Habashi, will remain there.
His lawyer, Stephen Watt, from the American Civil Liberties Union, said his client would be devastated.
"The fact that Binyam is being left behind in Guantanamo is really extremely disappointing and I know, having spoken to his brother here in the US, that that's going to come as a real blow to him," Mr Watt told BBC News.
Just over 300 prisoners are held at the facility, set up at a US naval base in Cuba after the invasion of Afghanistan in early 2002.
The US has argued that foreign nationals captured and detained outside the US have no recognisable constitutional rights.
Lawyer Zachary Katznelson, of human rights group Reprieve, which represents UK residents at Guantanamo, said all five British residents at Guantanamo had received "nothing at all in the way of justice".
"It's about time they were returned to their families and we're grateful to the British government for making this happen," he added.
THE FIVE DETAINEES
Omar Deghayes, pictured above, Libyan with refugee status
Shaker Abdur-Raheem Aamer, Saudi Arabian granted indefinite leave to remain
Jamil el-Banna, Jordanian with refugee status
Binyam Mohammed al Habashi, Ethiopian asylum seeker
Abdulnour Sameur, Algerian with leave to remain
Amnesty's UK spokesman Neil Durkin welcomed the move and said: "We will now be seeking to establish why Shaker Aamer is expected to go to Saudi Arabia, why Binyam Mohammed is apparently not set for return and why another former UK resident - Ahmed Belbacha - has not been mentioned in these reports."
British and US authorities have been in intensive negotiations about the men's return over the past few months despite the Pentagon insisting the men are all dangerous.
The US is seeking reassurances that they will not pose any security threat.
The Americans accuse Mr el-Banna of being a prominent al-Qaeda recruiter and financier, Libyan Mr Deghayes of associating with al-Qaeda, and Algerian Mr Sameur of receiving combat training in Afghanistan.
An official announcement on the releases is expected in the next few weeks.
The Foreign Office and Home Office, meanwhile, have refused to comment on the releases or when they might take place.
Lib Dem MP Sarah Teather, who serves Brent East where Mr el-Banna was living, said he had a five-year-old child who he had never seen because of his detention.
Ethiopian Binyam Mohammed al Habashi will remain at Guantanamo
She told BBC News: "The family would desperately love to believe that Mr el-Banna would be back for Eid which is just before Christmas but they know and I know that it could be months.
"As far as we know, no date has been set and we dare not get ourselves too excited yet about a forthcoming release."
The Conservatives have been asking the government whether they think the three men returning to the UK pose a threat and if so what security precautions will be taken when they return.
Shadow Security Minister Dame Pauline Neville-Jones said the government needed to be more upfront about what was happening.
"The Americans have not actually insisted we take these people, this is a voluntary action on the part of the UK and the government actually started this process last August, so they must know what they are going to do next and I do think they need to tell us rather than leave us to speculate."
The men have all either been granted refugee status, indefinite leave or exceptional leave to remain in the UK.
Foreign Secretary David Miliband formally wrote to his US counterpart Condoleezza Rice with the request for the men's release.
Last year the Court of Appeal upheld the government's decision not to request the return of non-British nationals because the US said it would not negotiate with third countries.
The Foreign Office also said such a move would be counterproductive to its aim of securing the closure of Guantanamo.
The foreign secretary and the home secretary said they requested the release of the men because of steps taken by the US government towards shutting down the detention facility.
The government said all British nationals had been released from Guantanamo by January 2005.
Lord Goldsmith, who negotiated for the release of Britons held at Guantanamo during his time as attorney general, said the UK had always acted as quickly as it could while following proper procedures in such matters.
He said that had included securing the release of all British nationals.
The UK had rejected the initial demands of the US that prisoners would only be given back if they were automatically detained back in Britain, Lord Goldsmith added.
"So I think we did take a principled and a proper stand - it took longer to get them back than I personally would have liked but at least they did come back," he told BBC News.
Meanwhile two cases being heard by the US Supreme Court are being seen as test cases over Guantanamo.
Two detainees are challenging the removal - by an act of US Congress - of Guantanamo prisoners' right of habeas corpus to take cases to US civilian courts.