“We have concluded that the UK chose to join the invasion of Iraq before the peaceful options for disarmament had been exhausted. Military action at that time was not a last resort.” That is the finding of Sir John Chilcot’s long-awaited inquiry into the Iraq War. The restrained mandarin language cannot obscure the scathing nature of the condemnation of Tony Blair and his associates in that adventure.

The Chilcot Report does not, in essence, tell us anything that most intelligent people did not already know. That does not mean its conclusions are otiose: on the contrary, it is essential that so great a blunder should be forensically analysed, its participants interrogated and the whole tragic jigsaw assembled as accurately as possible, though there will inevitably remain areas still open to speculation. Historians will find it an invaluable document, but its principal usefulness is in exposing to the light of public scrutiny at least some factual elements of what occurred.

The scale of the disaster was awesome. Chilcot assesses the war as causing the deaths of ‘at least 150,000 Iraqis – and probably many more – most of them civilians’. That is broadly in line with other estimates, though a Lancet survey calculated there had been 601,027 violent deaths in Iraq between 2003 and 2006. The aftermath was more lethal for the civilian population than the brief period of formal hostilities. Chilcot puts the number of displaced persons at ‘more than a million people’. A figure twice that size cannot be ruled out.

Behind these cold statistics lies a chronicle of death, terror and misery on a scale unseen back in Europe since 1945. While its magnitude might almost seem to dwarf British casualties of 179 killed and 315 wounded, some of them maimed, a moral imperative dictates the value of every human life. Professional soldiers accept they offer their lives as hostages to the vicissitudes of war when they enlist; but by the same token there is an obligation on every government not to commit its troops to combat unnecessarily.

Who, apart from Tony Blair and Alastair Campbell, will today claim the Iraq conflict was necessary? The “dodgy” dossier is now the discredited dossier – it already was even before Chilcot reported. The suggestion that Saddam Hussein’s battlefield missiles could have reached a British target (presumably Cyprus) “within 45 minutes” is patently absurd. Chilcot concludes that Saddam posed no imminent threat. That was obvious even in 2003.

The forces driving the chariot of war were American post-9/11 revanchism and a dynastic notion on the part of George W Bush that he had a duty to complete his father’s unfinished business from the First Gulf War by overthrowing Saddam Hussein. Add to that the militancy of the neo-conservative elements at that time controlling the US administration and the sabre-rattling from Washington was deafening. Post-9/11 the Americans wanted to strike at Middle Eastern targets, all loosely denominated al-Qaeda, although Saddam had been more effective at crushing an incipient al-Qaeda presence in Iraq than the coalition would ever be.

The terrorist attack on the New York Trade Center had deeply wounded America in its heart and soul. Its reputation as a super-power was compromised. Uncle Sam needed to kick some butt and Saddam’s seemed the most convenient. But no such considerations weighed on Britain, which had once governed Iraq and had some cultural understanding of the region. Tony Blair should at least have tried to impose a moderating influence; instead, he made himself complicit, writing to President Bush on 28 July 2002: ‘I will be with you whatever.’ His cabinet was unaware of this autocratic commitment.

It was Blair who suggested the casus belli to Bush: an ultimatum to Hussein to disarm. His reward was a medal and standing ovation from the US Congress and the familiar frat-boy greeting from Bush: ‘Yo, Blair!’ The immoral and distasteful nature of Blair’s conduct should not blind us to the underlying bathos: the pathetic quest of a fantasist for tinsel glory and the limelight.

Unhappily, one man’s photo opportunity is another man’s – or woman’s or child’s – nightmare. The devastation of Iraq is not only immense, but continuing. The Syrian civil war and the rise of ISIL is just one further aggravating element of a Western-provoked state of anarchy which, just three days before Chilcot reported, saw 250 people killed in a suicide bombing in Baghdad.

The Iraqi economy is struggling. Oil revenue has been siphoned off by corruption when it is most needed. In an optimistic moment in 2014 oil production rose to average 3.6 million barrels a day, the highest level since 1979, but that same year the Kirkuk and Bai Hassan oil fields were seized by Kurdish forces. ISIL, which holds most of the oilfields in neighbouring Syria, controls the Qayyara field near Mosul and briefly occupied the Ajil and Allas fields until driven out by the Iraqi army.

The oil price crash caused the fiscal and current account balance to implode in 2015. Iraq needed to build 2.5 million homes by this year to replace the destruction of war, but is likely only to achieve a small fraction of that figure. In rural areas only 77 per cent of the population has a modern water supply. The unstable state of the country is hardly calculated to attract investors.

Considering the postscript to a war in which little or no attention had been paid to a post-war settlement, where tens of thousands of schoolteachers were purged for having joined the Ba’athist Party under compulsion, the police disbanded and anarchy given free rein, it beggars belief that Western leaders moved on from this fiasco to enforce regime change elsewhere, e.g. Libya, and to applaud the fall of the West’s best friend, Hosni Mubarak, in Egypt. Only parliamentary opposition prevented David Cameron from taking military action against Assad in Syria, despite the evident fact his successors would be ISIL and other jihadist groups.

Will Western leaders ever be weaned off the fantasy that, if foreign tyrants are overthrown they will be replaced by democracy, probably in the shape of a Liberal Democrat/Green coalition? The shame of Tony Blair is Britain’s shame too: we permitted his actions and re-elected him for a third time even after the ravaging of Iraq. It was not an ‘illegal’ war, it was authorised by the formal mechanisms of British parliamentary democracy. That is the larger disgrace.