British troops have been accused of torturing and killing civilians in southern Iraq.
The claims - which the Ministry of Defence (MoD) strongly denies - are among the most serious yet levelled against British soldiers who served in Iraq.
Up to 20 Iraqi civilians may have been executed following a three-hour gun battle in the town of Majar-al-Kabir in May 2004, it has been claimed.
The allegations were first reported within weeks of the incident, known as the Battle of Danny Boy after a checkpoint where it took place.
Lawyers for five Iraqis have now issued detailed witness statements, photographs of corpses and death certificates of the men who died.
They are bringing a damages claim in the UK courts, and calling for an investigation by Scotland Yard.
Lawyers Phil Shiner and Martyn Day suggested that prisoners captured after the battle may have been taken to a British base at Abu Naji and killed.
They say the five witnesses are labourers who have lived all their lives in Majar and had "absolutely nothing" to do with the insurgent Mehdi army, who engaged British troops at the Battle of Danny Boy.
Detailed witness statements from the men - Hussein Jabbari Ali, Hussain Fadhil Abass, Atiyah Sayid Abdelreza, Madhi Jassim Abdullah and Ahmad Jabber Ahmood - described what they heard while in detention, when they say they were cuffed and forced to wear blacked-out goggles.
Mr Abdelreza's statement said: "I believed people were being killed. I have never heard anything like that sound ever before in my life.
"It shocked me and filled me with such terror."
While displaying photos taken following the gun battle, Mr Day said: "The nature of a number of the injuries of the Iraqis would seem to us to be highly unusual in a battlefield."
The solicitors have called for an ongoing investigation by the Royal Military Police (RMP) to be taken over by Scotland Yard.
"There is the clearest evidence available of systematic abuse and systematic failings at the very highest levels of politicians, the civil service and the military," said Mr Shiner.
A spokesman for the MoD said: "Allegations of mistreatment, unlawful killing and mutilation by British troops following an incident at Vehicle Checkpoint Danny Boy were thoroughly investigated by the RMP.
"Their investigation lasted ten months, involved the interviewing of over 150 British personnel and 50 Iraqi nationals, and found no evidence to support these allegations.
"New allegations are part of an ongoing RMP investigation and judicial review and it would be inappropriate to comment further."
