Mr Blair said the Iraq invasion would have been justified even without WMDs
The ex-director of public prosecutions has accused Tony Blair of "sycophancy" towards President Bush.
Sir Ken MacDonald called the 2003 Iraq war a "foreign policy disgrace of epic proportions".
He said the former prime minister had used "alarming subterfuge" to mislead the British people into the conflict.
Mr Blair told the BBC at the weekend that it would have been right to invade even if it had not been thought Saddam had weapons of mass destruction.
Referring to Mr Blair's interview with Fern Britton, Sir Ken wrote in The Times: "This was a foreign policy disgrace of epic proportions and playing footsie on Sunday morning television does nothing to repair the damage."
He said Washington had "turned his head and he couldn't resist the stage or the glamour that it gave him".
Sir Ken added: "It is now very difficult to avoid the conclusion that Tony Blair engaged in an alarming subterfuge with his partner George Bush and went on to mislead and cajole the British people into a deadly war they had made perfectly clear they didn't want, and on a basis that it's increasingly hard to believe even he found truly credible."
Sir Ken, who works at the same barristers' chambers as Mr Blair's wife Cherie, said: "Since those sorry days we have frequently heard him repeating the self-regarding mantra that 'hand on heart, I only did what I thought was right'.
"But this is a narcissist's defence and self-belief is no answer to misjudgement: it is certainly no answer to death."
The belief that Saddam Hussein had weapons of mass destruction was the key justification for the UK joining the US-led invasion of Iraq in March 2003.
No such weapons were found after the invasion and key bits of intelligence put forward by then Joint Intelligence Committee head Sir John Scarlett in the infamous 2002 weapons dossier later discredited.
Speaking on Fern Meets... on BBC One on Sunday, Mr Blair was asked whether the idea of Saddam having WMDs had "tilted" him in favour of war.
He replied that it was "the notion of him as a threat to the region of which the development of WMDs was obviously one" aspect.
Asked whether he would have invaded Iraq without the WMDs dossier, he said: "I would still have thought it right to remove him.
"I mean obviously you would have had to use and deploy different arguments, about the nature of the threat."
Mr Blair is due to give evidence in the New Year to the Chilcot inquiry into the war.
Sir Ken said the questioning so far by the panel had been "unchallenging", adding: "If Chilcot fails to reveal the truth without fear in this Middle Eastern story of violence and destruction, the inquiry will be held in deserved and withering contempt."