(Adam Sorenson/British Ministry of Defense, Pool, via AP, File) London - The head of Britain's Iraq War inquiry released a damning report on Wednesday on a conflict he says was mounted on flawed intelligence, was executed with "wholly inadequate" planning, and ended "a long way from success."Retired civil servant John Chilcot, who oversaw the seven-year inquiry, said "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 2.6-million-word report is an exhaustive verdict on a divisive conflict that - by the time British combat forces left in 2009 - had killed 179 British troops, almost 4 500 American personnel and more than 100 000 Iraqis.Chilcot said then-Prime Minister Tony Blair's government presented an assessment of the threat posed by Saddam Hussein's weapons with "certainty that was not justified." He also found military planning for the war and its aftermath were not up to the task."The people of Iraq have suffered greatly" because of a military intervention "which went badly wrong," he said. But he refrained from saying whether the 2003 invasion was legal, and did not find that Blair and his government knowingly misled Parliament or the British public."I will be with you whatever" - Blair to BushChilcot heard from 150 witnesses and analysed 150 000 documents. His conclusions are a blow to Blair, who told President George W. Bush eight months before the March 2003 invasion - without consulting government colleagues - "I will be with you whatever."The report says Blair went to war to stand shoulder-to-shoulder with Britain's main ally, only to find the UK excluded from most important decision-making about the military campaign and its aftermath."Mr. Blair, who recognised the significance of the post-conflict phase, did not press President Bush for definite assurances about US plans," the report concluded.Iraq descended into sectarian strife after the occupiers dismantled Saddam 's government and military apparatus, unleashing chaos that helped give rise to the Islamic State group.(Dan Kitwood/Pool via AP) The report found failings by military chiefs who did not provide adequate equipment to forces in the field, and whose main post-invasion strategy "was to reduce the level of (UK) deployed forces."The report concludes that Britain's combat mission, which ended in 2009, did not achieve the objectives laid out in 2003 and saw British forces make a "humiliating" deal with militias in southern Iraq to avoid attacks."The UK failed to plan or prepare for the major reconstruction program required in Iraq," the report said.Blow to BlairThe war has overshadowed the legacy of Blair, whose government has been accused of exaggerating intelligence about Saddam's alleged weapons of mass destruction in order to build support for the invasion.Chilcot criticised spy chiefs who failed to ensure their partial intelligence about Saddam's weapons was not hardened into certainty by government spin. He said they also failed to consider "that Iraq might no longer have chemical biological or nuclear weapons" - which turned out to be the case.The report said the widespread perception that the government had exaggerated intelligence evidence "has produced a damaging legacy, including undermining trust and confidence in government statements."Blair - who declined to comment on the report before publication - has always said his government did not invent or distort intelligence.The report also faults him for making key decisions with only a few key aides rather than through collective Cabinet consultation.Chilcot's report has been repeatedly delayed, in part by wrangling over the inclusion of classified material, including conversations between Blair and Bush. Some of Blair's pre-war letters to the president are published in Chilcot's report, but not Bush's replies.Anti-war activists and relatives of some dead British troops hoped the report would find the conflict illegal, opening the way for Blair to be prosecuted for war crimes.The International Criminal Court is looking into alleged war crimes by British troops in Iraq, but says has said that Britain's decision to go to war falls outside its jurisdiction.