In his annual State of the Union address last week, George W. Bush returned to a familiar theme - the grave danger the world is said to have faced from Saddam Hussein's biological and chemical weapons. Had it not been for the US-led invasion of Iraq, said Mr Bush, 'the dictator's weapons of mass destruction programmes would continue to this day'. The argument remains central to the coalition's justification for the war and the legitimacy of its occupation of Iraq. But the failure to find any weapons of mass destruction, despite months of searching, has weakened this position. And it was further undermined this weekend by the verdict of the man who was given the task of finding the stockpiles. David Kay has stepped down as chief of the Iraq Survey Group, responsible for tracking down the banned arms. His assessment, one which will not find favour with coalition leaders, is that no stockpiles of chemical or biological weapons existed when the invasion was launched last year. He believes that such weapons were in Hussein's hands at the end of the first Gulf war in 1991, but were subsequently destroyed. It is the most authoritative challenge yet to the claims that Iraq had to be attacked to remove an imminent threat to the world. His conclusions will add weight to allegations that suspect intelligence concerning Hussein's weapons was too easily relied upon and then exaggerated by US and British leaders in a bid to swing international opinion behind the invasion. While the hunt will go on, it is becoming increasingly unlikely that the feared weapon stockpiles will be found. The view gaining currency is that while Iraq did possess banned weapons, it probably disposed of them years ago. We can only speculate as to why Hussein might have taken such a course and then kept the rest of the world guessing as to whether the weapons existed. As officials in the US have been quick to point out, the failure to find the weapons does not rule out the possibility that Hussein was trying to acquire them. Mr Kay did uncover some evidence of active weapons programmes existing at the time of the invasion. That, however, is not the same as the existence of lethal hauls of chemical weapons ready to be deployed within 45 minutes - which is what the British government claimed. Mr Kay is to be replaced by former UN weapons inspector Charles Duelfer, who recently expressed his own doubts that weapons of mass destruction would be found. We hope he lives up to his pledge to discover the truth - whatever that may be. US Vice-President Dick Cheney said last week that 'the jury is still out' on the weapons issue. That may be true. But the jury - in the form of international opinion - is still lacking evidence and is becoming more sceptical by the day.