By Peter Biles
BBC world affairs correspondent
This will be remembered as the week when the Iraq Inquiry went "private" for the first time since the public hearings began in November.
Sir Jeremy Greenstock was tight lipped as he left the inquiry
There was no warning. Around midday on Tuesday, Sir Jeremy Greenstock, Britain's special envoy in Iraq in 2003/04, was in full flow, giving evidence. Suddenly, the video feed from the inquiry room was cut for just over 60 seconds.
The committee chairman, Sir John Chilcot, had taken advantage of the one minute delay on the broadcast to prevent some of Sir Jeremy's words being revealed. Three lines on page 68 of the Iraq Inquiry's official transcript were subsequently blacked out.
Sir Jeremy had been talking about his reports back to London whilst working in the Coalition Provisional Authority (CPA) in Baghdad with the US administrator, Paul Bremer.
A moment later at the hearing, he went on to say: "Secretary (Colin) Powell was reading the UK telegrams from Baghdad because he wasn't getting enough information from the Pentagon about what was really going on in Baghdad, as opposed to what Ambassador Bremer was reporting."
According to the transcript, the blacked-out sentence was "redacted on grounds of national security".
Was it a storm in a teacup, or had Sir Jeremy Greenstock, one of Britain's most experienced diplomats blurted out something that might have compromised UK security?
Such an indiscretion seemed highly unlikely. Leaving the QEII Centre, Sir Jeremy offered no explanation. He just smiled at the journalists outside, and muttered the word "immaterial".
Sir John Chilcot shed no further light on the matter. At the end of the hearing, he had said only that he had interrupted the broadcast because of "a mention of sensitive information".
It was unfortunate that the incident completely overshadowed the three hours of evidence given by Sir Jeremy Greenstock.
He provided an insightful account of the workings of the CPA in which Britain - in his words - had been "a low-quantity partner".
Sir Jeremy made it clear that his relationship with Paul Bremer was often difficult.
"He (Bremer) didn't want to hear suggestions about how to complete a satisfactory political process that were different from what the President had decided," Sir Jeremy told the inquiry.
The narrative of post-war Iraq took us right up until 2008 this week, but it was the witness evidence about the deteriorating security situation in 2003/04 that proved to be the most interesting.
This was when the UN headquarters was bombed, the Iraqi insurgency took root and when the abuse of Abu Graib prisoners occurred.
We heard about the US reluctance to use the term "insurgency".
The American Defence Secretary apparently gave orders that the word should not be used. Donald Rumsfeld had referred to those involved, not as insurgents, but as "a bunch of no-hopers carrying out some terrorist acts".
Sir John Chilcot is able to switch the inquiry into private mode
There was extensive detail about the challenging conditions that faced the British forces based in Basra.
Lt Gen William Rollo, the General Officer Commanding Multi-National Division South East in 2004, described southern Iraq as desperately impoverished.
"It is dirt poor by comparison to Kuwait on one side, but it is poor even by comparison with Baghdad. You go round Baghdad and you could be in Italy, large chunks of it anyway. It is developed, organised, and southern Iraq was not", said Rollo.
Some aspects of post-invasion Iraq have been raised again and again, such as the problem of reconstituting an Iraqi police force, and eradicating corruption.
In September 2003, Tony Blair said he wanted to see a decent police force running by the end of that year.
Sir Jeremy Greenstock and his predecessor in Baghdad, Sir John Sawers, warned Blair that it might take a year or so.
"It was an extremely ambitious request", said Sir Jeremy.
As the Iraq story falls into place, the Chilcot inquiry has found it easier to pose the right questions.
The committee is demonstrating a strong desire to assess the human, political and financial cost of this endeavour and finding out what lessons are to be learnt.
It is, at times, a deeply dispiriting story.
The unexpected speed of the Coalition's military success invading Iraq in March 2003, resulted in the huge problems during the aftermath.
Tony Blair's former Foreign Policy Advisor, Sir Nigel Sheinwald, was pretty frank: "I think all of us who started jobs in the summer of 2003 were conscious that we were arriving after the train had left the station".
So, he was asked, was Iraq worth the very high cost, especially in lives lost and people seriously injured? For once, an erudite Whitehall mandarin looked stumped.
"That's a very difficult decision and a very difficult debate and I can't answer that even now", he replied.
Even more surprising was the conclusion drawn by the current MI6 chief, Sir John Sawers. He admitted that had Britain realised how much violence would be unleashed in post-war Iraq, there might well have been "second thoughts" about the entire mission.
There is now plenty to ask Tony Blair when he appears before the Iraq Inquiry in the New Year.