Leading article: The challenge of Chilcot

That the Prime Minister is to appear before the Chilcot inquiry before the general election rather than after – as previously agreed – says much both about the course of the inquiry and the increasingly febrile political atmosphere. The start of the inquiry was greeted with widespread scepticism that anything useful would be achieved. The verdict two months into the hearings must be that, while it is uncovering little new, it is not at all a barren exercise.

Iraq remains a highly divisive issue and the way key participants saw events at the time (and may have edited their memories subsequently) adds a dimension that has not been heard in public before. Next week's appearance by Tony Blair is set to be prime box office. The challenge by the Liberal Democrat leader, Nick Clegg, at Prime Minister's Questions showed that it might now be more politically risky for Mr Brown to postpone his appearance than not. At least this is what No 10, rightly, appears to believe.