No nation state should relinquish it's right to act when faced with a potential threat. Judging by it past performance, no nation state should ever relinquish that right to the UN.

The US had received information from the Russians regarding Saddam Hussein's intentions post 9/11. The best way to counter those aims was to ensure that Iraq disarm itself and rid itself of all WMD in its possession and to verify that all programmes aimed at acquiring and developing WMD were shut down.

This may (or may not) be true. But if this is the case, then the US didn't attack Iraq under the terms of any UN resolutions, because there is no UN resolution that authorizes the US to attack Iraq during the timeframe in question. This means that the US preemptively attacked Iraq in violation of international laws and treaties, and it did so with no authorization other than its own say so. The US can't have it both ways. It's either acting in accordance with UN resolutions, or it's in violation of them. In this case, it's in violation of at least one. Since the US violated a UN resolution when it attacked Iraq, it should stop using UN resolutions as justification for it's war against Iraq.