Tony Blair used "deceit" to persuade parliament and the British people to support war in Iraq, Sir Ken Macdonald, the former director of public prosecutions, said today.

In an article in the Times, Macdonald attacked Blair for engaging in "alarming subterfuge", for displaying "sycophancy" towards George Bush and for refusing to accept that his decisions were wrong.

Macdonald's comments about Blair's decision to go to war are more critical than anything that has been said so far by any of the senior civil servants who worked in Whitehall when Blair was prime minister.

Macdonald was DPP from 2003 until 2008 and he now practises law from Matrix Chambers, where Blair's barrister wife, Cherie, is also based.

In his article Macdonald highlighted a remark Blair made in an interview broadcast yesterday about supporting the overthrow of Saddam Hussein regardless of whether Iraq had weapons of mass destruction to explain why he thought the former prime minister was guilty of deceit.

But Macdonald also expressed concerns about the Iraq inquiry, suggesting that some of its questioning so far had been "unchallenging" and that Sir John Chilcot and his team would be held in "contempt" if they failed to uncover the truth about the war.

Macdonald wrote: "The degree of deceit involved in our decision to go to war on Iraq becomes steadily clearer. This was a foreign policy disgrace of epic proportions, and playing footsie on Sunday morning television does nothing to repair the damage.

"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."

Macdonald said that Blair's fundamental flaw was his "sycophancy towards power" and that he could not resist the "glamour" he attracted in Washington.

"In this sense he was weak and, as we can see, he remains so," Macdonald went on.

"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 misjudgment: it is certainly no answer to death."

Macdonald said that, with the exceptions of some of the interventions from Sir Roderic Lyne, the questions asked when the Chilcot inquiry has been taking evidence from witnesses have been tame.

"If this is born of a belief that it creates an atmosphere more conducive to truth, it seems naive. The truth doesn't always glide out so compliantly; sometimes it struggles to be heard," Macdonald said.

Many commentators have criticised the fact that all members of the Chilcot team are establishment figures – Chilcot himself is a former permanent secretary – and Macdonald said the inquiry needed to prove its independence.

"In British public life, loyalty and service to power can sometimes count for more to insiders than any tricky questions of wider reputation. It's the regard you are held in by your peers that really counts, so that steadfastness in the face of attack and threatened exposure brings its own rich hierarchy of honour and reward.

"Disloyalty, on the other hand, means a terrible casting out, a rocky and barren Roman exile that few have the courage to endure."

Macdonald said Chilcot and his team needed to tell the truth without fear of offending the Whitehall establishment.

"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," Macdonald said.

Yesterday, in an interview with Fern Britton broadcast on BBC1, Blair said he would have backed an attack on Iraq even if he had known that Saddam had no WMD.

"If you had known then that there were no WMDs, would you still have gone on?" Blair was asked.

He replied: "I would still have thought it right to remove him [Saddam Hussein]".

Blair added: "I mean obviously you would have had to use and deploy different arguments about the nature of the threat."