The following correction was printed in the Guardian's Corrections and clarifications column, Monday 7 December 2009

This comment piece said that every member of the cabinet apart from Robin Cook and Clare Short signed up to the Iraq war. Clare Short was indeed a public critic of the preparations for war but on 18 March 2003 she voted for a motion that the government "should use all means necessary to ensure the disarmament of Iraq's weapons of mass destruction". The invasion of Iraq began on 20 March

Hurrah. It's Colosseum time again. The all-singing, all-dancing Chilcot inquiry into the Iraq war is in town at the QE2 centre, with ministers tossed to lions, spies eaten by bears and spin doctors hacked by muscle-bound gladiators. Britain's political community, bored at having to wait six months for an election, is baying for blood. The nation may lack bread, but at least it can have a circus.

It even has a star Christian, Tony Blair, who got us into the mess. The cry is for him to die, and die horribly. The camera must toy with his face in the dock, zooming in on the dripping brow, the writhing body language, the phoney meekness and the mendacity. Damned as a war criminal, Blair must be hung, drawn and quartered and his head impaled on a spike at Temple Bar. He must be Chamberlain after Munich, Eden after Suez. There must be nothing left of him but a puddle of sweat.

The same goes for the rest of them, Gordon Brown, the cabinet, John Scarlett, Alastair Campbell, civil servants, generals, bag carriers and tea ladies. Kill them all. The amphitheatre is packed with MPs and journalists, salivating as the gore runs into the sand. Not Nero in all his pomp staged a show like this one.

What else is Chilcot about? We know the truth. The report can be written in a sentence. Tony Blair went to war in Iraq because he lacked the guts to stand up to George Bush, say the invasion was not justified by facts or law, and refuse to join him in Baghdad. Despite being told to his face by Hans Blix that there were no weapons of mass destruction in Iraq, he deceived the cabinet and parliament and took his nation to war.

We know this from a dozen books and papers, from leaks and reports, from freedom of information requests and memoirs. Chilcot might dot an i and cross a t. He might reveal a memo or confirm a date. But to what end? We have been told how Blair took the decision by sofa government, twisting, dodging and distorting the constitution to get it through. We know how Downing Street crafted documents to scare the public into believing that the nation's security was under threat. We know that the army was left without equipment or planning. All this we know.

There have been two independent inquiries into the preliminaries of the Iraq war. Both Hutton and Butler in 2004 supplied mountains of material. Both were staged as show trials, but both correctly interpreted their remit as to ascertain facts and put them in the public domain. The fault of both was to proffer half-hearted conclusions as to who might, or might not, be to blame. That had the audience howling whitewash.

The Chilcot inquiry was set up in response to that criticism, but it can no more deliver accountability than could its predecessors. An inquiry is not a default mode of democracy. As Sir John Chilcot said yesterday, his is not a court of law and "no one is on trial". Indeed, yesterday's session suggested an academic seminar on the topic of paint drying. Yet a trial is what the public appears to want: indeed, a trial, a verdict, a sentence and an execution. It clamours not for facts but for retribution for the Iraq war. It wants not a smoking gun but body parts.

This is a clear and unsatisfactory clash of expectations. An inquiry is not public accountability but a substitute for it. The setting up of Chilcot was not British politics acknowledging responsibility for the Iraq war, but abdicating responsibility. The war may have been peculiarly Blair's in that he personally oversaw the preamble to it and took upon himself the burden of selling it to the electorate. But parliament and the wider political community cannot be detached from blame and thus exonerated.

With the exception of the then foreign secretary, Robin Cook, and the development secretary, Clare Short, every member of the cabinet signed up to the war and most MPs voted for it. They did so in defiance of what Cook, who knew the state of the intelligence, told them. They did so knowing that the attorney general's advice had smudges all over it and knowing that the weapons of mass destruction dossiers were "dodgy". Blair was no fool. He made sure that the House of Commons debated and voted for Iraq, and it did.

Parliament may now bay for Blair's blood, but it approved the war and its various select committees never once voiced dissent. It did so because Labour MPs were frightened for their jobs and wished to keep in with Blair, and because Tory MPs never oppose wars. Most of the media agreed with them, even after 2 million Britons marched through London opposing the invasion. The political community ultimately bought into Blair's war. Only now does it talk about "the lies that led us into Iraq" and seek to hold others responsible.

Going to war is a democratic assembly's most serious decision. It must account for it. Parliament must explain to the public why it supported Blair and his government in the spring of 2003. If they now consider themselves mistaken, even if they were misled, MPs cannot push responsibility on to a stage army of judges, civil servants and historians. They must debate the matter and reach the appropriate conclusion. If parliament decides that the cabinet collectively was to blame – as surely it must – then it should demand resignations. If it finds itself to blame, it should dissolve and submit itself to the judgment of the electorate, rather than outrageously telling Chilcot not to report until after next year's election.

Suppose Chilcot were to name and blame specific ministers and public servants and call for their impeachment as deceivers or even as war criminals. What does parliament do? There has been no formal trial or even parliamentary hearing. Do MPs call in the director of public prosecutions? Suppose Chilcot blames parliament, as he should. Does it again dissolve itself?

The answer is that it will do none of these things. Chilcot is performing an exercise in historical research. Parliament will do absolutely nothing with his report, as it is doing nothing about Blair's other war in Afghanistan, even when there is still time to stop more unnecessary bloodletting. To MPs Chilcot is merely a convenience for getting themselves off the hook.

It is to this that democratic accountability is reduced: long periods of silent inertia interrupted by occasional spurts of blood.