WMD probe on systems not peopleThe inquiry into intelligence on Iraq before the war will focus on systems rather than the actions of individuals.
The Butler Inquiry has also confirmed that all its hearings will be held in private to avoid giving the public a partial view of the evidence.
The inquiry committee will start taking evidence in April but will only discuss its work when it reports in the summer.
The Liberal Democrats say their refusal to take part in the inquiry has been vindicated by the latest news.
Tony Blair called the inquiry after mounting pressure, caused by the American decision to hold an inquiry, the remarks of former weapons inspector David Kay, and the failure to find any weapons stockpiles in Iraq.
Anybody with information for the inquiry, which is chaired by former cabinet secretary Lord Butler, is asked to come forward by 31 March.
The inquiry says it will "focus principally on structures, systems and processes rather than on the actions of individuals".
Mr Blair has said the judgement on whether military action was right has to stay with politicians rather than being decided by the inquiry.
And he has argued the inquiry should not be a re-run of the Hutton report, which cleared the government of embellishing its dossier on Iraq's alleged weapons of mass destruction.
Unlike the Hutton Inquiry, witnesses will be questioned by the committee, rather than legal counsel.
Lib Dem foreign affairs spokesman Sir Menzies Campbell told BBC Radio 4's Today programme the inquiry's latest announcement justified the concerns voiced by his party when it was set up.
He pointed to the focus on systems rather than individuals.
"That inevitably means that there will be no reference either to the competence or to the judgement of the politicians which took the decision that the only way to deal with Saddam Hussein and the threat it was said he posed was to take military action," he said.
"That, I do not believe, will satisfy the public, after all for whose satisfaction this inquiry has been set up."
The Conservatives insisted the inquiry's remit cover the way intelligence was used before the war, saying that meant politicians' actions would be investigated.
There will be great interest in what the inquiry makes of the way the claim weapons of mass destruction could be launched within 45 minutes, was presented in the September 2002 dossier on Iraq.
Some newspapers took this to mean that weapons could be launched against Cyprus within 45 minutes.
Even Mr Blair and Foreign Secretary Jack Straw have said they did not know it only referred to short-range battlefield weapons until after the decision was made to go to war.