A snippet from the 21 July 2002 Downing St memo:
US views of international law vary from that of the UK and the international community. Regime change per se is not a proper basis for military action under international law. But regime change could result from action that is otherwise lawful. We would regard the use of force against Iraq, or any other state, as lawful if exercised in the right of individual or collective self-defence, if carried out to avert an overwhelming humanitarian catastrophe, or authorised by the UN Security Council. A detailed consideration of the legal issues, prepared earlier this year, is at Annex A. The legal position would depend on the precise circumstances at the time. Legal bases for an invasion of Iraq are in principle conceivable in both the first two instances but would be difficult to establish because of, for example, the tests of immediacy and proportionality. Further legal advice would be needed on this point.
OK then, reasons for Bliar to go to war:
1. Individual or collective self-defence? NO
2. To avert an overwhelming humanitarian catastrophe? NO
3. Authorised by the UN Security Council? NO
I too was uneasy about the involvement of the UK, but one follows lawful orders in the military.