The Ministry of Defence says the claims have already been investigated
Claims that British troops tortured and killed civilian detainees in Iraq are being heard at the High Court.
A group of Iraqis wants the court to order a public inquiry into allegations that soldiers killed up to 20 captives.
Some of them, who were detained at the camp, say they were punched, thrown violently against a wall, hit by guards and denied water during interrogation.
The government says the 20 were killed during a gun battle and that military police have investigated the claims.
Defence Secretary John Hutton is opposing the application for judicial review, which is expected to last 15 days.
The case arose out of events which took place during the British occupation of south-eastern Iraq.
Iraqi civilians were detained following the "battle of Danny Boy", a fire fight between UK soldiers and Iraqi insurgents near the town of Majar-al-Kabir in Maysan Province in May 2004.
Rabinder Singh QC, appearing for the six Iraqis, told the court running battles at a number of locations around Danny Boy - a vehicle checkpoint - were triggered when soldiers were ambushed.
It is the Ministry of Defence (MoD) case that nine Iraqis were taken from the battlefield to Camp Abu Naji, a nearby British base, and all left the base alive, the court heard.
Mr Singh said the MoD had stated that the bodies of 20 dead insurgents were also taken to the camp to see if any could be identified as being among the persons suspected of earlier murdering six British soldiers.
It would be unusual and against normal practice for dead bodies to be taken from a battlefield and it still remained unclear who had given the order, he said.
He claimed evidence existed to support accusations by the group of six Iraqis that other detainees had been taken live to the camp, tortured and killed.
Mr Singh said the applicants believed teenage civilian Hamid Al-Sweady had been taken alive to Camp Abu Naji after being caught up in the firefight but that his was one of the bodies returned the day after the battle.
His uncle is among the six applicants.
The others - five survivors of the gun battle who were detained in the camp - had been regarded as enemy combatants and were subjected to "tactical questioning", said Mr Singh.
This was a process the British Army used at the time to "continue the shock of capture" and the five have reported various forms of ill-treatment, including hitting and being banged against walls while being taken to and from interrogation.
Mr Singh said: "Even on the [Defence Secretary's] own account, they were using methods of interrogation that at the least constitute arguable breaches of Article 3 (banning inhuman and degrading treatment) of the European Convention on Human Rights."
An interrogator had referred to using a rusty metal tent pole, about a foot long, to "bang on the table" during interrogations, the court heard.
Mr Singh told the court: "My clients say they were hit on numerous occasions, including with the tent pole."
This accusation was denied, he said.
Mr Singh said there was also evidence of suspects being subjected to the loud, disorientating sounds of "white noise" and being forced to strip naked in front of about 10 people, including a woman interpreter.
The Royal Military Police inquiry rejected the allegations of murder, torture and mutilation.
However, the Iraqi applicants say medical evidence shows that bodies returned to families had marks of torture and mutilation, including close-range bullet wounds, the removal of eyes as well as stab wounds.
Their lawyers are asking the court to declare there was a series of breaches of the human rights convention, including Articles 2, 3 and 5 which protect the right to life and the right not to be tortured, and also the right to liberty.