Tony Blair committed to an invasion of Iraq almost eight months before receiving parliamentary and legal backing, and began military action before diplomatic alternatives were exhausted, a much-awaited inquiry into the conflict has concluded.

The report by Sir John Chilcot, a former civil servant, amounts to an excoriating verdict on Britain’s political, military and intelligence establishments, all of which are heavily implicated for misjudgments and occasionally ineptitude. It reserves particular criticism for Mr Blair, the former prime minister.

The report, published on Wednesday after a seven-year investigation, is the most detailed assessment by any government of the decision to go to war in Iraq and management of the subsequent occupation.