Lawyers for some 190 Iraqis who claim they were abused by British troops in Iraq between 2003 and 2008 are pushing for a public inquiry.
Claims of beatings, sleep deprivation, and sexual and religious abuse are being presented to Britain's High Court in London on January 29.
They come from the testimony of Iraqis who say they were victims of abuse, or from relatives of Iraqi detainees.
The High Court is to decide whether the abuse came in isolated incidents or was systemic and authorized as policy. The hearing is expected to last three days.
British human rights lawyer Phil Shiner compiled the testimony at meetings with the victims or their families, held mostly in Lebanon. He has no doubts about their systematic nature.
"This isn't about a few bad apples," he said. "The interrogation techniques were taught and trained as policy here in the U.K."
Most of the alleged abuse took place while the prisoners were in custody. In some cases it allegedly resulted in the death of the detainee.
According to Shiner, there are also claims of abuse during "strike operations" by British troops on people's homes.
"Strike operations on homes [were] authorized with disproportionate force," he said. "Iraqis [were] routinely handed over to the U.S. and Iraqi authorities to face torture or the death penalty, the reckless use of lethal force following war-fighting rules of engagement during the U.K.'s occupation of southeast Iraq -- these are troubling state practices and systemic issues, with the root cause high up in the chain of command."
The Defense Ministry says a public inquiry is not necessary as it has launched its own internal investigation.
In 2011, a year-long independent inquiry found a "very serious breach of discipline" by British soldiers in the case of Baha Musa.
Musa was an Iraqi hotel worker who died in 2003 after suffering violence while in British army custody in Iraq.
With reporting by guardian.co.uk, the BBC, and Al-Jazeera