A tragedy of global proportions; a human, moral and political disaster; a catastrophic blunder that will forever stand as a monument to the arrogance and folly of leaders we once trusted; 179 British troops killed, together with countless Iraqi civilians; a whole region destabilised; terrorism on the march. It is almost impossible to overstate the consequences of Tony Blair's invasion of Iraq.

To a greater extent than many of us expected, Sir John Chilcot's Report is ferocious in its condemnation. Remorselessly he shows how Blair and his closest colleagues mishandled every single element of that misbegotten war.

We already knew about the 'dodgy dossiers' peddled by the government before the invasion. We also knew from a previous report – the Butler review – that our former prime minister was being economical with the truth when he falsely claimed that there was "extensive, detailed and authoritative" intelligence on Saddam Hussein's supposed weapons of mass destruction.

Now with brutal clarity Chilcot confirms the slithery dishonesty that took Britain into war. He confirms that the crucial intelligence information was flawed – but it wasn't challenged "as it should have been." In essence, the Joint Intelligence Committee was used as a political football, while the behaviour of Attorney-General Lord Goldsmith in advising on the legality of war was "unsatisfactory".

Moreover, almost a year before the invasion, Blair wrote to US President George W Bush assuring him that "I will be with you, whatever" – one of several exchanges suggesting that he was committed to military action long before he told Parliament or even his own Cabinet colleagues.

It gets worse. Sir John says we rushed into war before all the peace options were exhausted.

Some of Blair's Ministers were kept in the dark about what was going on. The Cabinet didn't discuss all the military options or implications. Our troops were sent in to action without proper preparation or the right kit. Many were killed because of inadequate equipment, such as the lightly-armoured 'Snatch' Land Rovers, which proved utterly useless against roadside bombs.

And after the battle? We left Iraq in a shambles and had no idea of how to turn it around. There was no plan. No idea of what to do next. Boneheaded American administrators simply sacked Iraqi soldiers, police officers and civil servants who had been loyal to Hussein. The result – predictably – was a collapse into anarchy, which Britain was helpless to prevent.

Today Iraq is a living nightmare, a nation sunk in misery, bloodshed and sectarian strife. Atrocities are a daily occurrence. Last weekend, for example, 200 people were killed in Baghdad, which Isis claimed responsibility for. There are so many such killings that only the most horrrifying of them are reported in the Western press.

Yes, it is true that there was appalling slaughter in Iraq long before Britain and America invaded.

As long ago as 1991, the Shia Muslim majority in Iraq rose up against Hussein's brutal regime, only to be butchered by the Sunni-majority Republican Guard. The Shia Marsh Arabs in particular, suffered a near genocide. So in fairness we shouldn't blame today's sectarian violence solely on Blair.

But it's hard to forgive him for not understanding that rash action in Iraq would make a bad situation worse. It's hard to forgive him for sending British troops into action more often than any other prime minister, while at the same time scrimping on military spending. And it's hard to forgive a policy that has squandered so many lives and increased the threat of terrorism.

Chilcot report
Demonstrators hold placards as they protest outside QEII Centre in London, as they wait to hear the outcome of the Iraq InquiryBen Stanstall/ AFP

So should he be prosecuted as a war criminal? The International Criminal Court has already ruled out any action, so that option can almost certainly be discounted. What happens next may depend on the families who have lost sons or daughters because of his policies. Time will tell whether any of them take legal action against him, and whether such action is successful

But whatever happens, let's not pretend that Tony Blair is the only culprit. This sorry episode exposes a serious malaise at the very heart of our political system, something that should concern us all.

Consider how easily Blair could get away with his habit of 'sofa government', in which crucial decisions could be made informally by a few ministers and their cronies, with no proper record-keeping and with other members of the government kept out of the loop. There couldn't be a better way of ensuring rotten decisions.

So how did most members of the government react when they discovered what Blair was up to? With tame feebleness, that's how. The late Robin Cook, to his great credit, resigned as foreign secretary, as eventually did Overseas Development Minister Clare Short. The others just kept their heads down.

Members of the security services were even more obliging. They co-operated in the production of dodgy dossiers and said nothing while Blair exaggerated the intelligence on Hussein's non-existent weaponry.

The civil servants? They said nothing either, with the honourable exception of Elisabeth Wilmshurst who resigned as a Foreign Office lawyer because of her doubts over the legality of the war.

And Parliament? Not only did MPs fail to hold Blair properly to account, but most of them took part in the most demeaning spectacle I've ever witnessed in the House of Commons.

On the day he left office as prime minister, politicians on both sides rose to their feet to applaud him, clapping him to the echo, as though they hadn't been misled, as though the war hadn't happened, as though the dead and wounded of Iraq no longer mattered.

So have we really learned the lessons of Iraq?

Leading the applause on the Tory side on that occasion was none other than David Cameron, a man who would one day topple another dictatorship in the Middle East, without considering the consequences. Libya is today a failed state and a haven for Isis.

So no. In spite of everything, I'm not sure we've learned any lessons at all.