Iraq changed everything for Britain: that’s why Chilcot matters so much

Strange to recall now, given the disaster that eventually engulfed him, but it was always said of Tony Blair that he was a lucky politician. Lucky in his timing, rising to the Labour leadership at the very moment Britain was ready to embrace almost any alternative to a stale Tory government; lucky in the opponents he faced; lucky that the economic sun shined for his entire 10-year spell in Downing Street, the skies clouding over within weeks of him leaving office. The timing of today's Chilcot report suggests Blair's luck has not entirely deserted him.

Related: What to expect from the Chilcot inquiry: revelation or whitewash?

Think of it. The Chilcot inquiry into the decision-making that led to the Iraq war was set up in 2009 and could have reported at any time in the last seven years. But it will come now, in the midst of the greatest political crisis to affect Britain since 1945. At any other moment, Chilcot would have been the all-consuming subject of national debate for days or even weeks, with Blair on the rack. Now, instead, it will fight for airtime alongside the battles for both the Tory and Labour leaderships and the raging argument about how Britain relates to its European neighbours. Blair's decisions will be exhumed, his reputation may well be flayed once more. But the focus will not be anywhere near as intense as the former prime minister must once have feared .

And yet if 23 June is indeed the most important British political event since the second world war, the 2003 invasion of Iraq is not far behind. Its legacy lives on, most obviously and most significantly for the people of Iraq and their neighbours. Those who live under the murderous rule of Isis or of Bashar al-Assad in Syria have every right to say it was the invasion 13 years ago that opened the gates of hell.

But its impact on Britain’s national life is huge and enduring too. First, whenever we talk about the lack of trust in our politicians, Iraq looms large. Of course, cynicism did not begin in 2003. But the experience of listening to Blair insist that the intelligence proved “beyond doubt” that Iraq had weapons of mass destruction – only for the US and British invaders to find none – has left many unable to believe a single word any politician says about anything. This was the prime minister, speaking about the most serious subject possible: peace and war. And yet what he said was untrue.

The expenses affair of 2009 fed the impression – mostly unfair – that MPs were in it only for themselves, greedily lining their pockets. But that sentiment grew upon the distrust that took root with Iraq. And that enduring suspicion is directed not only at politicians. Remember, Blair vowed that he had the backing of the intelligence agencies in pursuing his war against Saddam Hussein. And plenty of other figures of authority lined up behind him, including in the media. Why is it that during the referendum campaign Michael Gove could say that " people in this country have had enough of experts "? The answer partly lies in the sands of Iraq.

The party political legacy is no less clear. New Labour finds few defenders these days. Both right and left unite in trashing the entire project as a disaster. The Tories say Labour wrecked the economy; the current Labour leader speaks of the Blair period as one for which the party should atone . During the referendum campaign, Jeremy Corbyn refused to have any association , even indirect, with the predecessor who won three general elections: Corbyn would not even put his name to a pro-remain letter that had Blair's signature on it.

That's because of Iraq. The result is how rare it's become for anyone to speak up in favour of the rest of the New Labour legacy – from devolution in Scotland and Wales to peace in Northern Ireland, from Sure Start for kids to sharp reductions in child poverty. The shadow of Iraq is so great, it obscures everything else Labour did. So great was the catastrophe of Iraq, it's become impossible to salvage much else from the legacy of Blairism.

That's had a clear internal impact on Labour. Ed Miliband became leader in 2010 because he could distance himself from the Iraq decision. His brother could not. David was in parliament when the vote was taken, Ed was not. And that single fact made perhaps the decisive difference.

Related: Jonathan Freedland: The legacy of Iraq is that the world stands by while Darfur burns

Similarly, Corbyn's victory in 2015 was powered in part by his consistent opposition to the Iraq war: it distinguished him at a stroke from his rivals and allowed him to present himself as a total break with the past. Even now, as Angela Eagle and Owen Smith reportedly tussle over which of them should challenge Corbyn, Iraq is present. Smith supporters say Eagle would have no chance against the incumbent – because she voted with Blair in 2003.

The gravest legacy, however, reaches far beyond the politics of these islands. Until Iraq, there was support for the notion known as “liberal interventionism” – the belief that sometimes it’s right to deploy force to stop regimes from slaughtering civilians and especially their own people. After the Balkan wars of the 1990s, that idea had many supporters.

Iraq changed everything. From then on, the phrase was widely discredited , seen as a dishonest euphemism for western aggression. It meant that when Assad began unleashing brutal force against his own civilian population in 2011, there were few takers for military action in Syria. No one wanted to repeat the mistakes of Iraq. That reluctance came to a head with the Commons vote in 2013, when parliament heard David Cameron’s request to act – and said no .

So this is why Chilcot matters. Because the decisions taken in 2002-03 did not just lead to the loss of hundreds of thousands of lives in Iraq, creating the chaos in the region that led to Isis and the transformation of Syria into a slaughterhouse. It also dramatically altered the politics of this country. We live with its legacy every day.

guardian.co.uk © Guardian News and Media 2016