London : The UK joining the US-led invasion of Iraq in 2003 to outst dictator Saddam Hussein was not used as a “last resort” and was based on “flawed intelligence,” an inquiry into the war today said in a damning indictment of then prime minister Tony Blair’s decision to go to war.

The UK did not exhaust all peaceful options before joining the invasion of Iraq, said John Chilcot, the chairman of the official inquiry into the war set up in 2009.

“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,” the former senior civil servant told reporters.

He also said judgments about Iraq’s weapons of mass destruction “were presented with a certainty that was not justified” and post-war planning was “wholly inadequate”.

His 12-volume, 2.6-million-word report on the war on Iraq 13 years ago comes over seven years after the inquiry was ordered by then prime minister Gordon Brown.

About 180 British soldiers were killed in the Iraq war from 2003 to 2009.

Delivering a crushing verdict on Blair who was prime minister when the UK decided to go to war alongside the US to unseat Hussein as president of Iraq, Chilcot said, “When the potential for military action arises, the government should not commit to a firm political objective before it is clear it can be achieved. Regular reassessment is essential.

“The UK’s relationship with the US has proved strong enough over time to bear the weight of honest disagreement. It does not require unconditional support where our interests or judgments differ,” it said.

Chilcot’s long-overdue report spans almost a decade of UK government policy decisions between 2001 and 2009.

It covers the background to the decision to go to war, whether troops were properly prepared, how the conflict was conducted and what planning there was for its aftermath, a period in which there was intense sectarian violence.

In reference to the now-notorious “dodgy dossier” which had reportedly claimed Iraqi dictator Hussein, who was eventually killed during the conflict, had a stash of weapons of mass destruction, the report finds that intelligence had “not established beyond doubt” that Hussein continued to produce chemical and biological weapons.

The inquiry set out a note sent by Blair to then US President George W Bush on July 28, 2002, months before the invasion of Iraq, which indicates how early on the decision to go to war had begun to be crystallised.

Blair wrote “I will be with you, whatever. But this is the moment to assess bluntly the difficulties. The planning on this and the strategy are the toughest yet”.

Meanwhile, Prime Minister David Cameron told parliament after the report was released that lessons must be learnt from the UK’s decision to invade Iraq in 2003 to ensure that war is always the last resort.