Thirteen years after the start of a war which left Iraq in ruins, the region destabilised and tens of thousands dead, Britain will today learn the answers to lingering questions about its worst foreign policy disaster since the 1956 Suez crisis.
Sir John Chilcot’s 12-volume, 2.6 million-word report has been seven years in the making but the consequences of Tony Blair’s decision to join in the invasion of Iraq are being felt acutely in British politics today.
The lack of trust in the political establishment which found expression in last month’s EU referendum has many causes, including scandals surrounding MPs’ expenses.
But the decision to go to war in 2003 on the basis of souped-up claims about faulty intelligence dealt the biggest blow to politicians’ credibility.
The phrase "dodgy dossier", first used to describe the bogus claims made by Blair's government to justify the march to war, was thrown at prime minister David Cameron when his government warned about the likely economic impact of Brexit.
And the war not only destroyed Blair’s reputation but deepened divisions within the Labour Party which now threaten to tear it apart.
Much of the story of Britain’s involvement in Iraq has already been told, in two previous official reports, in the memoirs of some of the key players and in critical books about the conflict.
But Chilcot's inquiry, established by then prime minister Gordon Brown in 2009, had more sweeping powers and greater scope than earlier official investigations.
Prosecuted war
A retired civil servant who spent seven years as the most senior official at the
Northern Ireland
Office, Chilcot made clear from the start that his inquiry was not a court of law but promised not to flinch from expressing a view on the actions of those who ordered and prosecuted the war.
“The members of the committee are not judges, and nobody is on trial. But if the committee finds that mistakes were made, that there were issues which could have been dealt with better, it will say so,” he said.
The International Criminal Court in The Hague has ruled out prosecuting Blair for ordering British troops into action, on the grounds that the legality of the decision is beyond its remit.
The court said, however, that it would study the report for evidence that British service personnel may have committed war crimes in Iraq.
Chilcot’s five-person panel examined more than 150,000 documents and questioned more than 120 witnesses, including Blair and other senior politicians, top civil servants and military and intelligence chiefs.
The report will not rule on the legality of the war but it should cast fresh light on how the decision to go to war was made and the extent to which intelligence was used to bolster the case for a course of action Blair had already committed to.
The inquiry had access to emails between Blair and then US president George W Bush, as well as transcripts of Blair's side of their phone conversations.
Mass destruction
These could help to establish if, as his critics have long claimed, Blair promised to support the invasion before he had intelligence which could point to
Saddam Hussein
possessing weapons of mass destruction.
Saddam had no such weapons, and Chilcot sought to establish if Blair and others deliberately distorted or exaggerated intelligence reports to suggest that there was evidence that he did.
Besides the run-up to the war, Chilcot examined its conduct, particularly the British forces’ calamitous operation in Basra, in southern Iraq.
Relatives of some of the 179 British service personnel killed in Iraq have long complained that they were inadequately equipped and poorly prepared for the deployment.
Scotland's former first minister Alex Salmond said that, whatever the report concludes, those responsible for Britain's involvement in the Iraq war must be held to account.
“This report will not provide a verdict, and far from being the final word on the Iraq war it will just be the start of a process – providing some of the evidence and findings from which we can then determine those responsible,” he said.
“I want to reassure the families of those who died, and everyone living with the consequences of this conflict, that there is renewed cross-party determination to ensure Mr Blair and all those responsible for the lies and failures are held to account.”