Boris Johnson has said Tony Blair has "finally gone mad" after he insisted the 2003 invasion of Iraq has nothing to do with the country's current crisis.
The Mayor of London said Blair's views that the failure to sufficiently deal with the crisis in Syria is more responsible for the "nightmare" which is occurring in Iraq is so far separated from the truth that he "surely needs professional psychiatric help".
The criticism comes after Blair published an essay on his official website in which he rejected the "bizarre" claims that Sunni militants such as the Islamic State of Iraq and the Levant (Isis) would not be rising up in Iraq if the invasion supported by the former prime minister and US president George Bush did not take place.
Blair added the best way to deal with jihadist groups currently sweeping through Iraqi towns and cities is to intervene yet again.
"Where the extremists are fighting, they have to be countered hard, with force," he added.
The war in Iraq was met with huge protests and condemnation after it was based on the assumption the country had nuclear weapons, a theory which Johnson described as a "tragic mistake".
Writing in his column for the Daily Telegraph, Johnson said Blair's attempt to "rewrite history" by claiming Britain and the US are not responsible for the current conflict in Iraq is "frankly emetic".
He added: "The reality is that before the US-led invasion of Iraq in 2003, there was no al‑Qaeda presence in that country, none at all. Saddam was a ruthless Ba'athist tyrant who treated his population with appalling brutality. But he did not have anything to do with the 9/11 attack on the World Trade Centre, and he did not possess Weapons of Mass Destruction.
"The truth is that we destroyed the institutions of authority in Iraq without having the foggiest idea what would come next. As one senior British general has put it to me, "we snipped the spinal cord" without any plan to replace it.
"There are more than 100,000 dead Iraqis who would be alive today if we had not gone in and created the conditions for such a conflict, to say nothing of the troops from America, Britain and other countries who have lost their lives in the shambles."
He added: "The Iraq war was a tragic mistake; and by refusing to accept this, Blair is now undermining the very cause he advocates – the possibility of serious and effective intervention. Blair's argument (if that is the word for his chain of bonkers assertions) is that we were right in 2003, and that we would be right to intervene again."
Johnson concluded by suggesting that Blair "put a sock in it" with regards to commenting on Iraq.