Here is the full text of defence correspondent Andrew Gilligan's original report on BBC Radio 4's Today programme from 29 May, 2003.
John Humphrys: The government's facing more questions this morning over its claims about weapons of mass destruction in Iraq.
Our defence correspondent is Andrew Gilligan. This in particular, Andy, is Tony Blair saying they'd be ready to go within 45 minutes.
Andrew Gilligan: That's right that was the central claim in his dossier which he published in September.
The main case, if you like, against Iraq and the main statement of the British Government's belief of what it thought Iraq was up to.
And what we've been told by one of the senior officials in charge of drawing up that dossier was that, actually the government probably knew that that 45 minute figure was wrong, even before it decided to put it in.
What this person says is that a week before the publication date of the dossier, it was actually rather a bland production.
It didn't - the draft prepared for Mr Blair by the intelligence agencies actually - didn't say very much more than was public knowledge already and Downing Street, our source says, ordered a week before publication, ordered it to be "sexed up", to be made more exciting and ordered more facts to be, to be discovered.
Humphrys: When you say more facts to be discovered, does that suggest that they may not have been facts?
Well our source says that the dossier, as it was finally published, made the intelligence services unhappy, because, to quote the source, he said, there was basically, that there was, there was, there was unhappiness because it didn't reflect the considered view they were putting forward - that's a quote from our source - and essentially, the 45 minute point was, was probably the most important thing that was added.
And the reason it hadn't been in the original draft was that it was, it only came from one source and most of the other claims were from two, and the intelligence agencies say they don't really believe it was necessarily true because they thought the person making the claim had actually made a mistake - had got mixed up.
Humphrys: Does any of this matter now - all these months later - the war's been fought and won?
Gilligan: Well the 45 minutes isn't just a detail, it did go to the heart of the government's case that Saddam was an imminent threat and it was repeated four times in the dossier, including by the prime minister himself in the foreword.
So I think it probably does matter. Clearly, you know, if it was wrong - things are got wrong in good faith - but if they knew it was wrong before they actually made the claim, that's perhaps a bit more serious.
Here is the text of Gilligan's later conversation with presenter John Humphrys on BBC Radio 4's Today programme at 0732 on 29 May, 2003. It came after Downing Street denied Gillgan's earlier report.
John Humphrys: Tony Blair had quite a job persuading the country, and indeed his own MPs, to support the invasion of Iraq.
His main argument was that Saddam had weapons of mass destruction that threatened us all.
None of those weapons has been found.
Now our defence correspondent Andrew Gilligan has found evidence that the government's dossier on Iraq that was produced last September was cobbled together at the last minute with some unconfirmed material that had not been approved by the security services.
Now you told us about this earlier on the programme Andy and we've had a statement from 10 Downing Street that says it's not true.
And let me just quote what they said to you - 'not one word of the dossier was not entirely the work of the intelligence agencies' - sorry to submit you to this sort of English but there we are.
I think we know what they mean. Are you suggesting, let's be very clear about this, that it was not the work of the intelligence agencies?
Andrew Gilligan: No, the information which I'm told was dubious did come from the agencies, but they were unhappy about it, because they didn't think it should have been in there.
They thought it was, it was not corroborated sufficiently, and they actually thought it was wrong, they thought the informant concerned had got it wrong, they thought he'd misunderstood what was happening.
Let's go through this. This is the dossier that was published in September last year, probably the most substantial statement of the Government's case against Iraq.
You'll remember that the Commons was recalled to debate it. Tony Blair made the opening speech. It is not the same as the famous dodgy dossier - the one that was copied off the internet - that came later.
This was quite a serious document, it dominated the news that day.
And you open up the dossier and the first thing you see is a preface written by Tony Blair that includes the following words 'Saddam's military planning allows for some weapons of mass destruction to be ready within 45 minutes of an order to deploy them'.
Now that claim has come back to haunt Mr Blair because if the weapons had been that readily to hand, they probably would have been found by now.
But you know, it could have been an honest mistake. But what I have been told is that the government knew that claim was questionable, even before the war, even before they wrote it in their dossier.
I have spoken to a British official who was involved in the preparation of the dossier, and he told me that until the week before it was published, the draft dossier produced by the intelligence services, added little to what was already publicly known.
He said: 'It was transformed in the week before it was published, to make it sexier.
'The classic example was the statement that weapons of mass destruction were ready for use within 45 minutes. That information was not in the original draft.
'It was included in the dossier against our wishes, because it wasn't reliable. Most things in the dossier were double source, but that was single source, and we believed that the source was wrong.'
Now this official told us that the transformation of the dossier took place at the behest of Downing Street, and he added: 'Most people in intelligence weren't happy with the dossier, because it didn't reflect the considered view they were putting forward.'
Now I want to stress that this official and others I've spoken to, do still believe that Iraq did have some sort of weapons of mass destruction programme.
'I believe it is about 30% likely there was a chemical weapons programme in the six months before the war and considerably more likely that there was a biological weapons programme.
'We think Hans Blix down-played a couple of potentially interesting pieces of evidence, but the weapons programmes were small: sanctions did limit the programmes.'
The official also added quite an interesting note about what has happened as a result since the war of the capture of some Iraqi WMD scientists.
'We don't have a great deal more information yet than we had before. We have not got very much out of the detainees yet.'
Now the 45 minutes really it's not just a detail, it did go to the heart of the government's case that Saddam was an imminent threat and it was repeated a further three times in the body of the dossier.
And I understand that the parliamentary intelligence and security committee is going to conduct an inquiry into the claims made by the British Government about Iraq and it's obviously exactly this kind of issue that will be at the heart of their investigation.
John Humphrys: Andrew Gilligan, many thanks.