(BBC) As Tony Blair mulls over the findings of the Butler report, Gordon Corera considers the limits of international espionage:
I was in Amman, Jordan, a few months before the toppling of Saddam Hussein.
Across the hotel room from me sat a lanky, chain-smoking man nervously shifting in his seat. Every time someone came into the room he purposefully turned his face away so as not to be seen.
He was, he told us in halting English, a major in Saddam Hussein’s feared intelligence service, the Mukhabarat. He had recently defected and feared for his life.
At times arrogant and at times elusive, over one long evening he told his story: how before he left, his work was to keep watch on scientists to make sure they did not defect.
And from watching them, he said with a smile, he knew the secrets of the weapons of mass destruction programme.
He paused and waited for the next question, knowing what it would be.
He said he knew of trailers used as mobile biological production labs.
He then described, in fine detail, a trip he had made in the mid-1990s to Africa, to purchase nuclear material from the Russia mafia, giving the dates of travel for a roundabout route to make sure Western intelligence never found him.
The claims were explosive in the charged atmosphere before the war, but how could we know if he was telling the truth?
Checking his story out with the nuclear watchdog, the International Atomic Energy Agency (IAEA), created some doubts.
Suspicions were also raised once it became clear he was linked to one of the Iraqi exile opposition groups which had their own agenda in pushing the case for war.
And so his claims never made it onto the air.
But then just a week or so later, something strange happened.
War was inching closer and Colin Powell was giving his speech before the United Nations Security Council outlining the evidence that Saddam Hussein did indeed have proscribed weapons.
A central part of that case was the existence of mobile biological weapons labs. And who was one of the sources he cited as evidence?
It was unmistakably none other than the same former Iraqi intelligence major.
US intelligence was willing to base their case for war, in some part, on the same nervous, suspicious man I met in Amman.
But now, more than a year later, it emerges that one part of the American intelligence community had strong suspicions that he may have been lying and doubted his reliability.
Yet despite being “under suspicion”, he somehow found his way into Colin Powell’s speech.
Somehow, along the line, the quality control mechanism for who was to be believed broke down.
The UK’s Butler report, likewise, makes clear that the root of the failure often lay in unreliable sources who gave the intelligence community what it wanted to hear.
The caveat about some of them was lost in translation as the evidence was made public and later some sources were found to be unreliable.
But that still does not explain all the mystery about why every Western intelligence agency – not just Britain and America’s – got it so wrong.
Maybe one answer springs from another piece of “intelligence” about Iraq, again before the war.
The scene this time was the smoky lobby of a hotel in one of London’s leafier neighbourhoods. Another Iraqi exile, this time a former military officer, is trying to pitch his wares.
He said he and his friends had maps of Saddam Hussein’s secret tunnels and details of weapons programmes, but what he slid across the table to me were documents allegedly smuggled out from the Iraqi army.
They seemed to show that frontline troops were being kitted-out with chemical warfare protection suits and antidotes to nerve gas.
This time other experts said they believed the documents were genuine and so the story made it on air.
And why would the former Iraqi president be distributing the equipment unless he was preparing to use those fabled weapons of mass destruction?
Strangely enough, this story ended up being true.
As US and coalition forces pressed through Iraq, they found the suits and the nerve gas antidotes lying in the trenches, more often than not abandoned by the Iraqi army fleeing before the coalition onslaught.
So why did they have them?
Trying to answer that gets us back to the great mystery surrounding Iraq and perhaps also the reason why Western intelligence agencies all got it so wrong.
Put simply, what was Saddam Hussein up to? Why did he apparently give up most of his weapons of mass destruction programme yet still act like he had something to hide?
Was he bluffing about his weapons to try to maintain his grip on power? Was he himself misled by some of those around him?
Given the fact he had used those terrible weapons in the past, and the way he acted right up to his toppling from power, it is perhaps easy to see why intelligence analysts sitting in London or Washington believed that there really must be something there.
How could it be otherwise?
Perhaps the real lesson is that spies are not perfect and nor should we expect them to be.
Trying to peer into the murky world of a regime like Saddam Hussein’s Iraq and extract its darkest secrets is no easy task.
Understanding the limits of intelligence – that it cannot tell you everything – may be the best lesson from the British and American inquiries.