Tony Blair formed an unlikely alliance with George W. Bush to send British forces into Iraq, and 10 years on, the former prime minister is adamant he took the right decision.
The Labour premier and the Republican US president were both convinced of the need to act against Iraqi dictator Saddam Hussein and his alleged weapons of mass destruction (WMD).
However, these weapons never materialised and although Saddam was ousted within weeks of the March 2003 invasion, Iraq soon descended into chaos at the hands of insurgents and militia groups.
"I still believe it was right to remove Saddam," Blair told Britain's ITV television.
"We sometimes forget now what the regime was actually like and the devastation it caused.
"Hundreds of thousands of people died in his wars. He used chemical weapons against his own people."
Blair's name will be forever linked to the war in Iraq, and his rare public appearances in Britain are routinely dogged by protesters who want him tried for war crimes.
Joining the US-led invasion split his centre-left party and the country, sparking Britain's largest-ever public demonstration by up to two million people.
Blair admits conventional wisdom has now solidified on the invasion being a mistake.
In his 2010 autobiography, "A Journey", he accepted he will never change some people's minds -- while most do not want to listen any more.
"I have often reflected as to whether I was wrong. I ask you to reflect as to whether I may have been right," he urged readers before presenting his case.
"Many supporters will acknowledge I did it for the correct motives, but still regard it as 'the stain' on an otherwise impressive record," he wrote.
"And of course those who aren't supporters regard it as final proof of villainy.
"To the question 'Is Iraq better now than in Saddam's time?' there really is only one sensible answer: of course.
"All I know is I did what I thought was right."
Britain committed 45,000 troops to the invasion and afterwards took military control of the southern provinces, costing the lives of 179 British service personnel.
Since the invasion, at least 112,000 Iraqi civilians and several thousand more policemen and soldiers have died in the carnage, according to British NGO Iraq Body Count.
Blair insists poor post-invasion planning was not responsible for Iraq's descent into sectarian bloodshed.
"That's an easy way for people to park the argument in a place they feel comfortable," he told ITV.
The pre-invasion fears of humanitarian and ecological disaster did not materialise, he said, pinning the chaos on terror groups seeking to destabilise the state.
A decade on, Blair admits there are still "big challenges" in Iraq.
But while he accepts responsibility for his decisions, he stresses the price of inaction, saying Iraq today "would at least arguably be much worse" if Saddam and his family still ruled.
"People never ask to atone for the acts of omission," he said, citing massacres in Rwanda, Bosnia and Syria.
"Inaction also has its consequences."
Blair remains the focus of considerable hostility over Iraq.
An anti-war theatre event entitled "Ten" takes place in London next month, its mock-up poster featuring a grinning Blair taking a mobile phone picture of himself in front of a desert explosion.
Meanwhile a YouGov poll of 1,684 British adults on March 10-11 found that 53 percent thought the decision to go to war was wrong, while 27 percent thought it was right.
Half thought Blair deliberately set out to mislead the public over WMD, while 31 percent reckon he genuinely believed Saddam had a stockpile.
However, some 41 percent think Iraqis are better off now than they would have been under Saddam, while 21 percent say the reverse.
Blair says he cannot regret the decision to go to war.
"I can't say sorry in words; I can only hope to redeem something from the tragedy of death, in the actions of a life, my life, that continues still," he wrote.