Sir John Chilcot's inquiry into the Iraq war heard from its last witness in 2011.

In 2015, the announcement that findings will not be published in time for the General Election will cause many to draw their own conclusions, rightly or wrongly. Regardless of the individual's views on the conflict, delay is not good enough. The affair has the quality of farce.

Sir John's explanations in a letter to the Prime Minister are anything but illuminating. He states that "substantial progress" has been made since he last wrote to David Cameron in November 2013, and to Sir Jeremy Heywood, Cabinet Secretary, in May 2014. Then, however, government and voters alike are given a glimpse behind the veil.

"Until we have received and evaluated responses from all those who have been given the opportunity to respond," writes Sir John, "I cannot give an accurate estimate for how long it will then take to complete our work, but it is clear that will take some further months."

At this point, those untutored in the ways of Whitehall - and those who know better - are entitled to an intake of breath. The evaluation of responses is one thing. It might be open to debate, but is properly the business of an independent inquiry. What Sir John is saying, however, is that responses from certain people have not even been received.

What is the meaning of this? An invasion born of a false prospectus took place in March 2003. After much official and political prevarication, the Chilcot Inquiry began its work fully six years ago. Anyone who has an answer to criticisms contained in a draft report has had more than enough time, surely, to formulate a response. Instead, even now, heels are being dragged.

In previous years, the confidentiality of relationships with the United States was held up as an obstacle. Sir John makes this much clear: that issue has been dealt with, at least to his satisfaction. Subject to "a small number" of redactions, 29 of Tony Blair's notes to President George W Bush can be published, along with the records of certain conversations.

So what - or who - has caused still another delay? Mr Cameron and his ministers have taken refuge behind the independence of Chilcot, as though it would be inappropriate even to comment. The Deputy Prime Minister, Nick Clegg, gets closer to the nub of the matter when he calls the delay "incomprehensible". Has Sir John moved too slowly, or is the establishment protecting its own?

Surreal as it sounds, we are perilously close to requiring an inquiry into the inquiry. Voters have a right to know why and how we went to war. They are also entitled to know why unnamed individuals appear to have been so obstructive for so long. Sir Menzies Campbell was right in one regard yesterday when he argued that the inquiry model established by Lord Leveson, operating to a strict timetable, is far preferable to the Chilcot shambles.

The Iraq war and its aftermath have poisoned British politics for close to a dozen years. The mistrust engendered has ravaged the reputation of the political process quite as much as expenses scandals. Even at this late date the inquiry could have served as an act of purgation. Instead, it has come to symbolise the problem.