The family of a British resident detained at Guantanamo Bay has said news of his imminent release has ended five years of misery and worry.
Omar Deghayes was accused of committing terrorist acts
But Omar Deghayes's brother, Abubaker, said he would not celebrate properly until they had been reunited.
Scotland Yard refused to say whether Mr Deghayes and two other detainees, Jamil el-Banna and Abdenour Samuer, would be arrested on their return to the UK.
The Home Office said its first priority was protecting UK national security.
A fourth British resident is also to be released. Shaker Abdur-Raheem Aamer will go to his native Saudi Arabia.
But a fifth, Ethiopian Binyam Mohammed al Habashi, will remain in detention at Guantanamo Bay in Cuba.
According to BBC Washington correspondent Jonathan Beale, "differences" remain between the UK and US governments over Mr al Habashi. He says it appears the Americans are not prepared to release him but that the British government wants him brought back to the UK.
However, our correspondent does not think this disagreement will jeopardise the agreement between the two countries over the release of the other four men.
The Foreign Office said only that it was in detailed discussion with the US over the detainees and was in contact with their families.
Omar Deghayes, a Libyan refugee who had been living in Brighton since 1986, was arrested in Pakistan shortly after the fall of the Taleban, and transferred to Cuba.
He was accused of committing terrorist acts against the United States, but his lawyer said it was a case of mistaken identity.
His brother told BBC News: "It's been a terribly difficult five years of misery, worry and stress.
"We had no idea from one day to the other what's happening and no way of contacting Omar and no way of speaking to him.
"I'm very grateful and thankful again to this country for bailing us out a second time - the first was when we arrived as refugees."
THE FIVE DETAINEES
Omar Deghayes, 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
He also spoke of his concerns about how his brother, a trained lawyer, would get over five years of "torture and misery".
Family and supporters of Mr Deghayes in Brighton have fought a high-profile campaign for his release.
In August, the UK government first requested the release of the men, having previously refused to intervene as they were not British citizens.
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.
In a statement, Sandra Hodgkinson, deputy assistant secretary of defense for detainee affairs, said: "The United States government is pleased that the British government has taken the step to request resettlement of former residents in the UK.
"No final decision has been made in this matter. However, we are engaged in a robust dialogue with the British government.
"As the president has stated, we would like to move toward the day we can close Guantanamo.
"We hope the international community will follow the lead of the UK, and accept detainees for resettlement who have been approved for transfer or release."
The Americans accuse Mr el-Banna of being a prominent al-Qaeda recruiter and financier and Algerian Mr Sameur of receiving combat training in Afghanistan.
The UK government has not confirmed the men are to be released but an official announcement is expected in the next few weeks.
The Home Office said: "The home secretary and the government are foremost fully committed to protecting the national security of the UK.
"It would be inappropriate to comment on any individual security measures that may be necessary.
"Should individuals be returned to the UK, the same security considerations would apply to them as would apply to any other foreign national in this country."
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."
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.
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.