The last British resident to be held in Guantanamo Bay has been released, having been detained there for 13 years, the foreign secretary has said.
Philip Hammond said Shaker Aamer had left the US military base and will return to the UK “later today”.
The Saudi national, 48, was held in the military prison in Cuba since 2002 but has never been charged or put on trial.
Mr Aamer, who has four children, has permission to live indefinitely in the UK because his wife is British.
He was detained in Afghanistan in 2001. US authorities alleged he had led a unit of Taliban fighters and had met former al-Qaeda leader Osama Bin Laden.
But Mr Aamer maintains he was in Afghanistan with his family doing charity work.
Since 2007 Mr Aamer, who claims he was tortured, has been cleared for release twice, first by US president George W Bush and then Barack Obama.
His plane is expected to land at London’s Biggin Hill airport at around 13:00 GMT.
Andy Worthington, co-director of the We Stand With Shaker campaign, said he was “delighted” Mr Aamer’s “long and unacceptable ordeal has come to an end”.
Mr Aamer, who is reported to have health problems, will require “psychological and medical care” when he returns to his family in London, he added.
In letters sent to the BBC by his lawyers earlier this month, Mr Aamer described himself as “an old car that has not been to the garage for years”, saying the first thing he wanted once freed was a cup of coffee.
“I have known nothing about the real world for more than 13 years,” he wrote.
By Dominic Casciani, BBC home affairs correspondent
When the business jet carrying Shaker Aamer lands in London he is likely to be met by British officials and detectives.
But if his case is handled like other returning detainees, he will soon be free to go on his way.
His lawyers say he will need medical and mental assessments. He may, like others who have been held at Guantanamo, be suffering from post traumatic stress disorder.
It’s unlikely we will ever find out if MI5 does decide to monitor Mr Aamer – by definition its work is secret.
On a human level, Shaker Aamer’s return is the end of the UK’s involvement in Guantanamo. But it’s not the end of the story.
The government’s long-promised investigation into substantial allegations that our agencies were mixed up in rendition and torture hasn’t happened – and many people are still demanding answers.
Raffaello Pantucci, from the Royal United Services Institute defence think tank, said Mr Aamer was likely to be interviewed by police and then monitored after he returns.
However, if he is not engaging with any illegal activity he would then be left alone by the security services, Mr Pantucci added.
Mr Aamer’s release has been welcomed by human rights groups and a number of MPs.
Kate Allen, from Amnesty International, said Mr Aamer had been held in “intolerable circumstances for nearly 14 years.
Cori Crider, from Reprieve, who is also Mr Aamer’s lawyer in America, said he now needed to “see a doctor and then get to spend time alone with his family”.
Labour leader, Jeremy Corbyn MP, tweeted his release was “great news”, while Conservative MP Andrew Mitchell said Mr Aamer must receive “full support” on his return to the UK.
Tory MP David Davis said he was keen to speak to Mr Aamer, saying: “I am sure many more MPs, look forward to seeing what he has to say about his detention.”
Former Guantanamo Bay detainee Moazzam Begg tweeted his “heartfelt thanks to everyone who fought for him”.
Mr Aamer’s imminent release was confirmed by the UK government last month, when his daughter, Johina, 17, tweeted: “We can’t believe we might finally see our dad after 14 years.”
Mr Aamer was detained in Afghanistan in 2001 by bounty hunters tracking down and handing over possible al-Qaeda suspects, shortly after the 9/11 attacks on America.
He was detained on the same day his son was born and has never seen him.
Mr Aamer was first held by the US forces at Bagram air base, near Kabul, where his lawyers say he was tortured. They say he made false confessions to end his torture.
However, US officials accused him of being a “member of al-Qaeda tied to the European support network” and a “close associate” of Bin Laden himself.
In February 2002, Mr Aamer was transferred to Guantanamo Bay, where his lawyers say he suffered further abuse.