Former Prime Minister Tony Blair will give evidence over his involvement in the Iraq war at the official inquiry into the war.

It is claimed he tried to persuade Gordon Brown to allow witnesses to give evidence in private.

Brown was forced to abandon plans for a behind-closed-doors probe after he received complaints from senior military and political figures.

Sir John Chilcot, the former civil servant, and his four-strong panel, have set out the terms of reference for the process. The inquiry is expected to last at least a year.

Sir John said the inquiry will be "as open as possible".

He added: "If we find on going through the evidence that we see... that people fell short in their duty, made mistakes, acted wrongly, we shall most certainly say so and say so clearly."

Only some elements of the inquiry which could pose a "grave" threat to national security will be made private.

Sir John said his "first priority" is to hear from the families of British service personnel killed during the conflict, along with veterans' groups and others affected.

Sir John, who was a member of Lord Butler's 2004 inquiry into the intelligence used to justify the invasion, had also been looking into ways to put witnesses under some form of "oath". When questioned about this, Chilcot said those giving evidence will not be under oath.

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