http://www.ukwilpf.gn.apc.org/cndpressrelease23jan03.html

If, as appears likely, the UK is involved in the use of force against Iraq the leaders of the UK Government will be investigated by the prosecutor of the international Criminal Court (ICC) if it breaches international humanitarian law (IHL). So promise a coalition of professors of law and leading NGOs from around the world. The UK,US and Canadian Governments have today been served with letters before action warning them of the consequences of an illegal use of force against Iraq. In the UK, Tony Blair was served at 10 Downing Street during filming for a Channel 4 TV programme on January 31.
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Go read it.
You know you want to.
Also the letter to Geoffrey Hoon at the bottom of the page.