PB: Well I would begin, I hope this doesn’t strike you as hopelessly pedantic; I would begin by distinguishing between pre-emption, preventive war and preclusion because they’re often melted together in the popular mind. Pre-emption is a well-recognised strategy in international law; it is not unlawful. It depends upon the presence of an imminent attack, an attack that is truly imminent. It does not require the target state to wait for the attack. Preventive war is something altogether different. Preventive war is a belligerency undertaken to prevent a worsening geostrategic or geopolitical ratio or correlation. Pearl Harbour would be a good example of preventive war. And it is pretty generally considered in international law as illegal.

Preclusive war is warfare that is undertaken not in the face of an imminent attack but not unilaterally either. It is undertaken when by legal standards the target state has rendered itself liable to intervention and I suppose Bosnia would be a good example of that. Nobody really thinks, I suppose, that the Serbs in Bosnia threatened Nato (they certainly didn’t threaten Washington) or that the Serbs in Kosovo threatened Washington. One of the problems with the Iraq war, I believe, was the feeling that we had to say, or it was felt by some that they had to say, that an imminent attack was faced by London or by Washington or by New York. Of course this was crazy; it wasn’t true. I don’t mean, by the way, that I think the war was illegal but I do mean that the basis on which some advertised it simply showed the poverty of legal concepts in this area.

MG: It’s not an analogy I’ve used before and it may be completely inept but trying to get Saddam purely on this technical question is like trying to get Al Capone on tax evasion. I’m not saying that possession of nuclear weapons of mass destruction is a minor misdemeanour but that because for a variety of reasons we all now know this was the lowest common denominator around which you could secure agreement both within the American administration and broadly within the West and that skewed the whole debate about Iraq. There are historical examples where states, specifically Britain, have intervened to prevent weapons falling into the wrong hands. We intervened in the Napoleonic wars to stop the Danish fleet falling into Napoleon’s hands – Canning intervened there. Churchill intervened to sink the French fleet at Oran in 1940 to stop Vichy handing over effective control of the Mediterranean to Hitler and Mussolini. So as a democracy fighting for survival and seeking to demonstrate to our allies that we were serious about fighting a long war, we as a country have taken pre-emptive action to stop weapons falling into the wrong hands. It isn’t a doctrine that was cooked up or confected to justify Iraq. It has a long pedigree and whatever one might argue about those individual actions, history vindicated the people who took them.