Lots of his weapons were dismantled one way or another in the fist Gulf War, how on earth did he reassemble the apparatus to manufacture these weapons later on?
That's not the issue, the issue is that he conspired to interfere and in some cases halt weapons inspections.
Whether he had them or not could not be fully ascertained because of his actions, not the UN's or the UK/US. Did it suit the UK/US agenda, of course it did, but inventing evidence, why bother and if they had, why not simply "plant" the required evidence after the fact?