The head of the inquiry into the Iraq war has said it was "crucial" key decision-makers gave evidence in public as he confirmed Tony Blair would be among the witnesses called.

Sir John Chilcot said his five-strong panel would "not shy away" from criticising anyone found to have made mistakes.

He added the process, which could take until 2011, would be open "wherever possible".

Critics raised fears Mr Blair and others could escape the spotlight after Sir John said some sessions could be behind closed doors to ensure "complete candour" as well as to protect national security.

But the inquiry chair, speaking at the formal launch of the probe, said that was simply designed to persuade less high-profile individuals to share information and opinions without being exposed.

"The formal giving of open oral witness testimony is crucial for the key actors and decision-makers," he said - opening the prospect of some being televised and streamed online.

"But there is a wide range of people with useful background knowledge we shall want to talk to on different terms," he told reporters.

Rose Gentle, whose son Gordon died in Iraq, responded to the news. She said: "We are actually a lot happier about what came out today than what Gordon Brown wanted.

"Gordon Brown wanted it all behind closed doors. I have never had any questions answered that I want answered, so that is why I think we will get this to put our questions forward as to why we did go in. Families need a closure. If we don’t get questions answered we are never going to get closure."

The inquiry, which will cover the entire eight-year period from the build up to the war to the withdrawal of British troops, was announced by Prime Minister Gordon Brown last month.

But the PM was forced to rapidly abandon plans for it to sit behind closed doors and not apportion any blame to individuals amid a cacophony of protest from senior military and political figures.

Sir John added: "We are determined to be thorough, rigorous, fair and frank to enable us to form impartial and evidence-based judgments on all aspects of the issues,"