The four men — the last of the British detainees at Guantanamo — were accompanied by anti-terrorist officers on a British military flight and landed at the Northolt Royal Air Force base, west of London, just after 5 p.m. (noon EST).
Moazzam Begg, Feroz Abbasi, Martin Mubanga and Richard Belmar were among some 550 prisoners from 42 countries swept up in the U.S.-led war on terror and detained without charge.
Security was tight at the airbase with a strong police presence.
Mubanga, a former motorcycle courier from north London, and Begg, who moved to Afghanistan to set up a language school, have claimed they were tortured while in custody — allegations dismissed by U.S. authorities.
Guantanamo holds detainees that U.S. authorities said were suspected of having links to the al Qaeda terrorist network or Afghanistan's ousted Taliban regime.
The decision to release the four followed months of sensitive negotiations between Washington and London to address U.S. security concerns.
The British government has said it will be up to police whether to arrest the men on their return to Britain and question them about possible involvement in terrorism.
Five other Britons were released from Guantanamo in March, and were not charged with any offense on their return to Britain. Four of them have filed a lawsuit in a U.S. court seeking $10 million each in damages.
A British Muslim group welcomed the return of the last Britons held at Guantanamo.
"These returnees have been through an appallingly lengthy and unjust ordeal in which they were deliberately held in a legal black hole by the U.S. authorities," the Muslim Council of Britain said in a statement. "The priority now must be for these returnees to receive immediate counseling and medical help."
Moazzam Begg's father has expressed concern about his son's mental health because of his detention.
"He was kept in solitary confinement for about three years and sustained solitary confinement is not a joke, it is a big thing," Azmat Begg told British Broadcasting Corp. radio.
His son had suffered "mental torture for three years and I don't know what that has done to him," he said. "Also, at the same time, I am happy my son is coming home."