The British government is to hold a "fully independent" inquiry into its involvement in Iraq that will have "unprecedented scope" but will be held behind closed doors, Prime Minister Gordon Brown said on Monday.
"No British document and no British witness will be beyond the scope of the inquiry," said Brown. "The inquiry is essential so that by learning lessons we will strengthen the health of our democracy, our diplomacy and our military," he added.
However, evidence would be heard in private so that witnesses, including politicians and military leaders, could be as "candid as possible".
Anti-war groups and relatives of some of the 179 British soldiers who died in the conflict immediately attacked the decision that the inquiry would be private.
Rose Gentle, whose 18-year-old son Gordon was killed in Basra in 2004, said she feared all her "agony could be for nothing."
"We have fought and fought for this but it will be no use and it could all be for nothing behind closed doors," she said, adding that her group would lobby parliament to "make sure this is all
The inquiry will go back as far as to 2001, covering the run-up to the 2003 invasion, the conflict itself and the reconstruction of Iraq following the final withdrawal of British forces at the end of July.
However, the investigations would take a year to complete and its results would therefore not be published and debated before the next general election, due by June, 2010, said Brown, drawing criticism from the opposition parties.
Brown conceded that the events of the past six years had been "complex and often controversial," but said they had nonetheless replaced a "vicious dictatorship" in Iraq with a "young democracy."
Brown said a total of 120,000 British servicemen and women had done service in Iraq since the joint Anglo-American invasion of March, 2003.
Of them, 179 had died and more than 220 had suffered serious injuries.
The inquiry is expected to shed some light on the process of political decision-making in the run-up to the invasion and investigate the apparent lack of a "post-invasion" strategy by the coalition.
It is likely to examine the policy decisions taken by then prime minister Tony Blair and look at the vexed issue of the so-called Iraq dossier, which alleged the existence of weapons of mass destruction under Saddam Hussein.
Lindsey German, spokeswoman of the Stop The War Coalition, said nothing short of a full public inquiry, leading to possible prosecutions, was required.
"There needs to be a full public inquiry to find out exactly why we were taken to war and to investigate the discussions between Tony Blair and George Bush in 2002."
"We need to know the thinking behind the dossier, and the lies, of weapons of mass destruction as well as the involvement of ministers, including Gordon Brown, who financed the war as chancellor."
However, Brown made clear that while the investigation, to be led by former top diplomat John Chilcot, would have access to the "fullest range of information, it would exlude "material essential to our national security."