Three British men held by the US in Guantanamo Bay for more than two years have compiled a report alleging abuse and humiliation while in captivity.
Asef Iqbal, Ruhal Ahmed and Shafiq Rasul allege humiliating and abusive treatment
The document, to be released in New York on Wednesday, was being passed on to the Senate Armed Services Committee.
The accusations include beatings and one of the men, Ruhal Ahmed, claimed a US guard pointed a gun at his head, in front of a British interrogator.
The UK Ministry of Defence said it would investigate any such allegations.
Asef Iqbal, Ruhal Ahmed and Shafiq Rasul - all from Tipton in the West Midlands - returned to Britain in March having spent more than two years without legal representation in American custody - first in Afghanistan, then at Guantanamo Bay.
They were then released without charge by British police.
Their experiences in captivity now form the basis of a 115-page report, Detention in Afghanistan and Guantanamo.
The allegations include:
- they were repeatedly punched, kicked, slapped, forcibly injected with drugs, deprived of sleep, hooded, photographed naked and subjected to body cavity searches and sexual and religious humiliations
- one American guard told the inmates: "The world does not know you're here - we would kill you and no-one would know"
- Mr Iqbal said when he arrived at Guantanamo, one of the soldiers told him: "You killed my family in the towers and now it's time to get you back.
- Mr Rasul said an MI5 officer had told him during an interrogation that he would be detained in Guantanamo for life
- the men said they saw the beating of mentally ill inmates
- another man was left brain damaged after a beating by soldiers as punishment for attempting suicide
- the Britons said an inmate told them he was shown a video of hooded men - apparently inmates - being forced to sodomise one another
- guards threw prisoners' Korans into toilets and tried to force them to give up their religion
The men allege that when a new camp commander, Maj Gen Geoffrey Miller, took charge, new practices began, including the shaving of beards, playing loud music, shackling detainees in squatting positions and locking them naked in cells.
Mr Ahmed said Foreign Office officials "did not seem to care or even ask him about the conditions".
The report says: "It was very clear to all three that MI5 was content to benefit from the effect of the isolation, sleep deprivation and other forms of acutely painful and degrading treatment, including short shackling.
"There was never any suggestion on the part of the British interrogators that this treatment was wrong."
The Foreign Office said the United States had been asked to examine the allegations and would be responding to them fully.
But a spokesman said none of the Britons at Guantanamo had made it aware of any allegations of systematic abuse, either when they were detained in the camp or on their release.
A statement said: "Throughout we have sought to meet the twin objectives of pursuing the fight against international terrorism whilst safeguarding the interests of the British citizens detained aboard."
All three men said they had made either written or verbal complaints to British embassy officials while they were being held.
The trio said they had eventually wrongfully confessed to appearing in a video with al-Qaeda chief Osama Bin Laden and Mohammed Atta, one of the 11 September hijackers.
Mr Rasul was actually working in a Curry's electronics store in the West Midlands at the time the video was filmed, the report says.
In the report, it is understood Mr Ahmed says shortly after his capture in northern Afghanistan in 2001 he was questioned by a British interrogator, who identified himself as an SAS officer, while an American soldier held a gun to his head, threatening to shoot him.
The UK Ministry of Defence acknowledged that such behaviour is contrary to the Geneva Conventions and has promised to investigate any such allegation.
For its part, the Pentagon has dismissed the claims of abuse as a fabrication.
Lawyer Gareth Pierce told BBC News: "There was not a single method that was not used to break their will to make them confess to something they were not guilty of, and all three did."