|Eliza Manningham-Buller made it clear that Iraq posed little threat prior to 2003 [AFP]
The UK's Iraq Inquiry has been marked by politicians and former senior British government officials either defending positions or, perhaps, massaging history to fit their purpose.
Many commentators have found it either deeply disappointing or even boring.
So the evidence of the former head of MI5, the British domestic intelligence service, on Tuesday, came as a significant intervention.
Elizabeth Manningham-Buller was head of MI5 before the Iraq war and for some time after it, and was privy to the internal discussions the government had with its intelligence services at the highest levels.
She made it clear, right from the start of her evidence, that MI5 saw Iraq as either a "very limited" or "containable" threat - and that she, as well as the CIA, had no belief that they were helping al-Qaeda before or after September 11.
MI5, she said, refused to submit any intelligence to support a case for war because she felt it was so thin.
She also suggested that the former US defence secretary Donald Rumsfeld set up a new intelligence body at the Pentagon because he wanted it to find a rationale for war which was otherwise lacking.
Her remit was to protect Britain from attack, and she said she made it very clear to the British government that war would increase the threat level.
But even she failed to realise the extent to which the Iraq conflict would radicalise British muslims.
She said Iraq became a "single narrative" - that the West was attacking Muslims and therefore Islam, and a section of a "whole generation" of British Muslims became radicalised because of it.
She linked the 7/7 attacks on London, Richard Reid's attempted shoe bombing, and other incidents, as having a direct line back to the Iraq conflict.
She went further still - arguably, she said, the West gave Osama bin Laden a gift - his Iraqi jihad.
By the end of 2003, after the ground war, MI5 had had a big budget increase, had opened eight new offices around the UK and were "swamped" with intelligence on new threats in the UK - more, she said, than we could cope with.
Did she raise any of these concerns before the war with Tony Blair, the-then prime minister?
No, she said, she had access only to the British home secretary, whom she reported to directly.
Perhaps, with hindsight, she said, she should have challenged the remit for war more than she did.
But she said the government view of the time was that even if war led to an increased threat of reprisal in the UK, it shouldn't stop them doing what they thought was right.
In the end it became a narrative which undercut the rationale for war (she said the threshold needed to be high and that intelligence was always "fallible") and which suggested that, contrary to claims from others, Britain and elsewhere are not now safer countries for Saddam being gone.
The remit of the inquiry is to try to learn lessons from the Iraq conflict for future British governments: it'll be interesting to see what credence the inquiry team give to her conclusions.