Shaker Aamer, the last British resident detained in Guantanamo, has been reportedly released and is flying back to his wife and four children in London.
Foreign Secretary Philip Hammond confirmed to Sky News Mr Aamer had been released. His plane is believed to be due to land in the UK at around midday today.
Co-director of the We Stand With Shaker campaign Andy Worthington also said he had confirmation from Mr Aamer's lawyer he is due to return.
"We're delighted to hear that his long and unacceptable ordeal has come to an end," he told Press Association.
"We hope he won't be detained by the British authorities on his return and gets the psychological and medical care that he needs to be able to resume his life with his family in London."
Cori Crider, Mr Aamer's US lawyer and strategic director of Reprieve, said in a statement the release was "long, long past time."
"Shaker now needs to see a doctor, and then get to spend time alone with his family as soon as possible.”
Amnesty International UK director Kate Allen cautioned: “After so many twists and turns in this appalling case, we won’t really believe that Shaker Aamer is actually being returned to the UK until his plane touches down on British soil."
“We should remember what a terrible travesty of justice this case has been, and that having been held in intolerable circumstances for nearly 14 years Mr Aamer will need time to readjust to his freedom," Ms Allen said in a statement.
The 46-year-old Saudi Arabian citizen has been held in the US dentention centre for 13 years without trial. His case was debated in the House of Commons in March, and MPs have lobbied Washington to urgently address his transfer – which was cleared in 2007.
Prime Minister David Cameron has personally lobbied on behalf of Mr Aamer, urging Barack Obama to free the Guantanamo detainee in June of this year.
A Downing Street source claimed Mr Cameron told the US president: "We are very clear we need to find a resolution to the case of Shaker Aamer."
On Friday, Labour leader Jeremy Corbyn congratulated Mr Aamer's team on the release, calling it "great news."
Mr McDonnell told The Mirror he was "breathing a heavy sigh of relief" following Mr Aamer's release. "Shaker was simply a man in the wrong place at the wrong time, a charity worker building wells in Afghanistan who was kidnapped, ransomed and falsely imprisoned."
Mr Aamer, whose British wife and four children live in London, has British residency and permission to reside indefinitely in the UK. He has not seen his family in 14 years.
He was imprisoned in Afghanistan after being accused of working with al-Qaeda.
A Reprieve report, published earlier this year, detailed the horrific torture he claims US interrogators meted out in an attempt to make him sign a false confession. Mr Aamer later said he would have told interrogators “he was Bin Laden” to make the torture stop.
Dr Emily Keram, an American doctor who was able to visit him in Guantanamo, diagnosed Mr Aamer with acute post-traumatic stress disorder (PTSD), migraines, digestive problems, swelling, asthma and tinnitus. She recommended urgent treatment for the “serious medical concerns” in the UK.
Guantanamo Bay detention centre was established in 2002 by the US government. Following a successful Freedom of Information request, the centre admitted to holding 779 men and boys over the course of its use. Mr Obama had promised to close the facility - condemned globally by international human rights organisations - but as of June this year 116 individuals remain imprisoned in the centre. That number will now stand at 115.