The long-awaited official report into Britain's involvement in the Iraq War has delivered a scathing verdict on British government ministers' justification, planning and conduct of a military intervention which "went badly wrong, with consequences to this day", The Telegraph reported on Wednesday.

British former prime minister Tony Blair presented the case for war in 2003 with "a certainty which was not justified" based on "flawed" intelligence about the country's supposed weapons of mass destruction (WMD) which was not challenged as it should have been, found report author John Chilcot.

Unveiling his 2.6 million-word report into the UK's most controversial military engagement since the end of the Second World War, Chilcot said: "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."

In 2002, Blair visited US former president Bush at his country retreat in Crawford, Texas. The report states: “Blair offered President Bush a partnership in dealing urgently with the threat posed by Saddam Hussein. He proposed that the UK and US should pursue a strategy based on an ultimatum calling on Iraq to permit the return of weapons inspectors or face the consequences.”

In July 2002, the UK Government had concluded that President Bush was “impatient to move on Iraq and that the US might take military action in circumstances that would be difficult for the UK”, the report states.

According to the report, Blair then wrote the crucial note to President Bush guaranteeing British backing “whatever”.