Shaker Aamer was captured in December 2001 by the Americans, who claim he was fighting with the Taleban.
Reprieve, the human rights group which was representing him, maintains he was sold by villagers to the Northern Alliance, who in turn sold him on to the Americans.
In a statement made
to his London lawyers, Birnberg Peirce, Aamer says he was taken to a prison at Bagram Airbase - a US camp in Afghanistan - in 2002.
In his own words, Aamer alleges: "After a few days of sleep deprivation they took me to the interrogation room and the intelligence team started coming one after another and the room was full, up to 10 or more.
"One of them, a British MI5 agent, was standing and they started talking to me in different languages - English, French, Arabic - and shouting. I started shouting with them and after that I do not know what happened.
"All I know is that I felt someone grab my head and start beating my head into the back wall - so hard that my head was bouncing. And they were shouting that they would kill me or I would die. After this, they left the room and told me to think and tell them the truth or I would die."
He says he was left alone with a gun on top of a table: "I did not know what to make of this. Do they want me to kill myself or do they want me to touch it so they can shoot me and say that I tried to shoot them? I was just sitting looking scared."
During these torture interrogations, Aamer says he made false confessions before he was moved to Guantanamo Bay on February 13, 2002.
His lawyers claim his ill-treatment continued at Guantanamo Bay and included beatings, sleep deprivation, exposure to extremes of temperature, force feeding and years of solitary confinement.
