Nearly 200 Iraqi civilians are fighting a High Court battle for a fully independent public inquiry into allegations that British troops committed "terrifying acts of brutality" following the invasion of Iraq.
Two judges were told women, the elderly and children were among the victims as soldiers went in search of individuals to detain and interrogate.
A judge-led inquiry is being sought into accusations that British interrogators were guilty of unlawful killings as well as torture in British-controlled detention facilities between 2003 and 2009.
Defence Secretary Philip Hammond is investigating the claims of human rights violations through the Iraq Historic Allegations Team (IHAT).
But Public Interest Lawyers (PIL), representing 192 Iraqis, argues the abuse was "systemic" and wants the High Court to rule that the IHAT set-up is fatally flawed because its members include officers of the Royal Navy Police (RNP).
Michael Fordham QC said the Royal Navy played "a significant role" in interrogations and IHAT was not sufficiently independent.
The QC told Sir John Thomas, president of the Queen's Bench Division, and Mr Justice Silber it was necessary "for somebody independent to grasp this nettle and pursue the truth of what happened, and its implications, compatibly with the rule of law".
This is the second legal challenge against IHAT. Last year the Court of Appeal ruled it lacked "the requisite independence" because it included investigators from the Royal Military Police, and they were replaced with RNP members.
MoD lawyers say the claim that the RNP presence threatens IHAT's independence is "inconsistent" with the appeal court decision.
They also say setting up a wide-ranging public inquiry now would be "inefficient, premature and disproportionate", arguing that such an inquiry could be set up at a later date if evidence of systemic abuses emerges. As well as the 192 Iraqi civilians represented at London's High Court, there are more than 800 others also making allegations of human rights violations.