AS JUNO begins her orbit round one gas giant, Head of Zeus offers a powerful perspective on another. You won’t read the Chilcot report in its entirety, or even its bulky summary, but you really ought to read Peter Oborne’s devastating indictment.

It targets not just Tony Blair, but also Jack Straw, a wobbly Attorney General, and large sections of the British Parliament and fourth estate, who fell for – or jumped in behind – Blair’s cynical rationalisations for military intervention in Iraq.

Oborne is hardly writing revisionist history. There are few now who believe that Blair comes out of the Iraq invasion with much integrity, but Oborne’s terse, forensic narrative points to a still more depressing conclusion: that in rolling over for the Americans, and abandoning his own seeming instinct for a legal solution to the Iraq situation, endorsed by the United Nations, he lost the chance to stand out as one of the more honourable statesmen of the last 100 years. But, of course, the Republican Party was softer on “axis of evil” dictators than it was on the hated UN, and Blair seems to have fallen under the ‘fluence while a guest at Bush’s Crawford ranch.

Like the Jupiter mission, the Chilcot Report is a numbers game, not just in terms of ordinance holding and putative WMD, but in length and pagination, too.

It took Sir John two more years to deliver than it took to get a vehicle to the middle of the solar system. The Jet Propulsion Lab’s surveyor is the fastest manmade object yet, Chilcot already a byword for legalistic immobility. Much is made in Oborne’s publicity and in news reports of the length of the target text, which is variously given as three, four and five times the pagination of War and Peace. It sounds like a reasonable literary comparison, except that the content is less Tolstoyan than Dostoevskian, less about grand movements of men and arms than about the pathology of leaders.

Not The Chilcot Report is said to be 50 times less bulky than the official version. It’s written with Hemingwayesque economy, albeit with a hefty crop of footnotes, most of them pointing to the painful fact that this fifth inquiry into the Iraq war has to trail in the wake of well-attested confirmations of Blair’s guilt. It makes for odd reading alongside the final unfolding of the Pistorius trial, where again there seemed to be a consensus for guilt long before the legal process found itself ready to admit that possibility.

It’s in a footnote that the most striking summation of the whole story can be found. It comes in a remark made to Oborne by the estimable Hans Blix, whose weapons inspectors could have resolved the whole matter without a shot being fired. He says that Blair’s assertion that there were WMD in Iraq was unsupported by evidence. “Both the UK and the US replaced question marks by exclamation marks”. Could it be better put than that? In 2002, Iraq came a slow fourth in most intelligence estimates of risk from “terrorist” states. She was, in fact, more of a danger to herself and to her citizenry than to any adjoining power, let alone the US and UK. Most of her illegal weaponry was either destroyed – on the orders of Saddam’s son-in-law Hussein Kamal – or in the case of chemical weapons had degraded beyond the point of use. Kamal defected to Jordan in 1995, briefed weapons inspectors, and then returned to Iraq, where he was executed; just another collateral victim, and just one more in the unagreed Iraqi casualty list, which veers between 100,000 and 1,000,000, depending on how you cook the figures.

And this all because Blair, Straw, their legal advisers and military men, took marker pens to the available evidence, none of which was seriously alarming, and then added the notorious exclamation mark of 45 minutes’ deployment time to the imaginary arsenal. All because George W. had a burning desire to finish what Pappy had started a decade before and left undone. Oborne’s previous books include The Rise of Political Lying. He couldn’t have asked for a more blatant illustration.

Chilcot’s pious hope that his multi-decker analysis would make it harder for the nation to go to war again without full legitimacy under international law sounds like the kind of “never again” mantra that is murmured annually at cenotaphs.

It misses the point – an even more significant point in the murky backwash of a Brexit majority – that Britain’s mystical constitution allows a UK prime minister to ignore law, parliament, morality and sensible advice and go to war like a tinpot dictator.

Not The Chilcot Report by Peter Oborne is published by Head of Zeus, priced £10