MPS who kept Baha Mousa's case in the public eye last night demanded a wide-ranging investigation into all allegations of brutality by British troops.
There are about 40 cases claiming brutality and unlawful killing of Iraqi civilians by the British Army. Many disturbing details have been documented by charities such as Amnesty International. But the alleged ill-treatment of Mr Mousa, 26, and seven other men arrested with him, has come to be regarded as a test case of British justice in Iraq.
Sir Menzies Campbell, the Liberal Democrat foreign affairs spokesman, said: "This [the ruling] is a slap in the face for the Government and a sharp reminder of its legal obligations. We pride ourselves in the good behaviour of British soldiers in Iraq, which in virtually every instance has been respected. But there are nagging suspicions that a very few servicemen wearing British uniforms have transgressed."
Harry Cohen, the Labour MP for Leyton and Wanstead, said: "I very much hope the Government won't appeal - that would be a callous act - and will accept this judgment."
The High Court's ruling is a blow to the Prime Minister and his Defence Secretary, Geoff Hoon, who had both tried to block a fresh inquiry.
Mr Hoon's lawyers had argued that an investigation could not be held under the provisions of the European Convention on Human Rights because that did not apply to British troops in south-east Iraq.
Christopher Greenwood QC, for the Government, had said there were territories in the world for which the European Convention on Human Rights was not designed.
But the judges described this as "an unhappy submission to have to make about a country which was one of the cradles of civilisation". They said: "No one knows to whom the baton or batons of the human race will be handed. The convention was not created because of the humanity of Europe, but because of its failures."
Instead, the court held that the UK's obligations under the Human Rights Act extended to "outposts of the state's authority" in foreign lands - and that included prisons operated by British troops.
An independent inquiry will now investigate whether there has been unlawful killing and breaches of Articles 2 and 3 of the convention, which guarantee the right to life and freedom from torture and inhuman and degrading treatment. It is expected to include 10 more cases of alleged ill-treatment. Further claims have made by six men who were detained at the same time as Mr Mousa.
Evidence before the High Court alleged that the men were forced to wear hoods and beaten, and that they were deprived of water and kicked across a room by soldiers.
The Mousa family could be entitled to damages from the British Government if breaches are proved. The family's lawyer, Phil Shiner, hailed the judgment as "a historic day for human rights and the rule of law in the UK".
He called for the immediate appointment of a British judge to investigate all the allegations of torture made against British soldiers serving in Iraq, including the case of Baha Mousa, "the most terrible of all".
But the judges rejected applications for judicial review made by five other families of Iraqis allegedly unlawfully killed by troops in south east Iraq after the cessation of major hostilities in May, 2003.
Dismissing their claims to independent investigations under the Human Rights Act, which incorporates the European convention into domestic law, the judges said the claims arose "out of shootings of Iraqis by British forces in the field".
The victims were not in custody and the deaths were on Iraqi territory which was outside UK jurisdiction and "outside the scope of the convention and the Act".
The Ministry of Defence welcomed the court's decision to reject five of the six cases but refused to comment further on the Mousa case because a prosecution in relation to it was still under consideration.
An MoD statement said: "In court, we argued that the ECHR [European Court of Human Rights] was never intended to cover the circumstances we face in Iraq where the security situation does not permit all deaths to be investigated in the same way as would happen in peacetime Europe.
"We welcome the court's acceptance of the general principle that any application of the ECHR outside the United Kingdom is exceptional and limited and occurs only in specific cases recognised in international law.
"This decision is important for current and future operations since in Iraq, where UK armed forces are regularly fired on and regularly return fire in self-defence, [and] it is not possible for us to adopt procedures such as the immediate establishment of a police cordon to enable the painstaking collection of forensic evidence."
A spokesman for Amnesty International said: "We're pressing the UK authorities to conduct independent, thorough and prompt investigations that fully comply with their obligations under international law."