The High Court in London has heard claims that British troops routinely abused detainees in Iraq in the years following the American-led invasion.
Lawyers representing 192 Iraqis asking for a public inquiry into British detention practices between 2003 and 2008 say the abuse appears to have been routine.
The court will decide whether alleged mistreatment was systemic, the BBC reports.
It will also consider whether an inquiry set up by the defence ministry is independent enough to investigate.
As well as unlawful killings, there are claims of beatings, hooding, sleep deprivation and sexual humiliation including being made to watch pornography.
Women, the elderly and children were among the victims, according to an 82-page document presented in court.
Lawyers said they were still collecting allegations of abuse almost a decade after the invasion of Iraq, and had hundreds of further claims in the pipeline.
The hearing before two judges is expected to last three days.