Carne Ross is a man with too much to say to mince his words. Britain's erstwhile first secretary at the UN saw a lot of how Britain got into the Iraq war, but his evidence to the Chilcot inquiry went much further, with some very harsh words for the inquiry itself.

The classic establishment inquiry, especially one with "lessons learned" as its highest aim, finds that mistakes have been made but that everyone did their best and no one lied. Previous Chilcot witnesses have played this game and, while it remains to be seen whether the inquiry will play along, they have rarely been challenged. Ross (not Sir Carne, you will note) is now saying pretty bluntly that people lied before the war and are still lying and that Chilcot is not equipped to deal with it. That's what happens when you let a known whistleblower in.

In a very hard-hitting written statement, Ross has again made clear that he did not see any case for war, either on the basis of the supposed failure of the policy of containing Iraq or based on the threat from its alleged weapons of mass destruction. On the first point, he is very well-placed to challenge the claims of previous witnesses, having been responsible for negotiating the policy at the UN until the middle of 2002. On the latter, he was less well-placed, although he does say that he saw all the intelligence.

Ross said it was "inaccurate to claim, as some earlier witnesses have done, that containment was failing and that sanctions were collapsing". This claim was made from the first day of the inquiry, by witnesses such as Sir William Patey, who, Ross points out, said that sanctions were "leaking all over the place". In a footnote, Ross says that "this was not the official assessment at the time and is a judgment that is not borne out in the relevant policy documents".

Ah, the documents. Ross rams the point home at the end of his statement when he addresses the inquiry's failings:

"It is striking that in my preparations for this testimony, I found several documents germane to the inquiry whose existence was not revealed by earlier witnesses, including those who authored them. Other documents by certain officials contradicted the testimony they have given at this inquiry and yet these witnesses were not questioned about these contradictions."

Ross uses his statement to reveal the contents of some of the documents that he has seen. But he has also been censored: "I was informed by the inquiry staff that I was not in public session to refer to or reveal the contents of classified documents which I reviewed in preparing my testimony." Two of his footnotes have been "redacted on grounds of international relations".

When it comes to the threat allegedly posed by Iraq, Ross says this was "intentionally and substantially exaggerated in public government documents", notably by the drafters of the September 2002 Iraq dossier. It happened "in a way that allowed those participating to convince themselves that they were not engaged in blatant dishonesty. But this process led to highly misleading statements about the UK assessment of the Iraqi threat that were, in their totality, lies."

Elsewhere, Ross talks of possible "perjury" by Chilcot witnesses and of "mendacity". These are not the sort of words you are supposed to use at an establishment inquiry.