Dr Hans Blix said the secret info they gave didn't help him find any evidence that Saddam Hussein was developing illegal weapons.
There's now a growing row about whether there was actually enough proof to go to war with Iraq.
Still searching
A new American-led team's just arrived to hunt for weapons.
Dr Blix said his team went to the places which were supposed to contain weapons - but they found nothing.
'Disappointed'
He told the BBC he was disappointed with the information provided by US and British officials.
Dr Blix, who is retiring from his job next month, said he still wasn't sure whether Iraq had weapons of mass destruction.
The US has defended the information it provided.
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Matthew's from Ark Royal diaries
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Dad's come home from Iraq!
