If, in its 150-page opinion, the International Court of Justice in the Hague declines to make a ruling or rules it is permissible to use or threaten to use nuclear weapons, or if it produces a "fudge", it will damage the court's legitimacy. Its judges will be accused of kowtowing to the five nuclear powers which are all permanent members of the UN Security Council. A ruling that nuclear weapons are legal would also open the way for other states to possess and test them, undermining the nuclear non- proliferation treaty and attempts to conclude a Comprehensive Test Ban Treaty.
If the court rules the use or threat of use of nuclear weapons to be illegal, the policy of deterrence upon which US, British and French security and, to a lesser extent, that of Russia and China have rested for decades will be in violation of international law. Nuclear deterrence is the policy of Britain's present Conservative government and, Tony Blair said two weeks ago, of a future Labour government.
Such a ruling would also challenge the legal status of the five permanent members of the Security Council, whose membership is rooted in their possession of nuclear weapons. It would strengthen demands that other criteria should determine permanent membership - such as economic strength or contributions to UN peace-keeping operations.
There would be other implications, thrown into sharper focus by the forthcoming 50th anniversary of the Nuremberg trial verdicts. If the use of nuclear weapons is declared illegal, the captain of a Trident submarine ordered to fire a nuclear missile will know that if he does so he can be indicted for a war crime.
The use of chemical weapons is now illegal, even in self-defence, and so are biological weapons - bacteria and viruses. So are laser weapons designed to blind people. There has been prolonged debate about outlawing land mines. But nuclear weapons remain outside and above the law.
On 15 December 1994 the UN General Assembly decided, by a clear majority, to ask the court - the world's supreme judicial body - whether "the use or threat of use of nuclear weapons is in any circumstance permitted under international law?". It is the first time non-governmental organisations have persuaded the General Assembly to use the World Court as an avenue to challenge the Security Council. It is also the first time the court has been asked to give its opinion on the legality of any weapon.
Most members of the UN believe nuclear weapons should be banned. Some 45 states gave evidence, two thirds arguing for illegality. Four of the five nuclear weapons states gave evidence: China declined.
The move to declare nuclear weapons illegal has been problematic, partly because they are crucial to the defence policy of certain states, and partly because they share certain characteristics - destruction by heat and blast - with conventional weapons. The move to declare them illegal has centred on other characteristics: the destruction caused by radiation and electromagnetic pulse, and their long-term damage on health and the environment.
The Nato nuclear states and Russia tried to dissuade the court from ruling on the question, pointing out that it was, in France's words, "an essential problem... one which is at the core of the national defence systems of a large number of states". France is probably the most strident opponent of the action. Britain also wants the court to decline a ruling.
The court's decision, expected at about 11am today, could go either way. The World Court should comprise 15 judges but, following the death of one, there are only 14. Those representing the five nuclear powers and two others are expected to support the legality of nuclear weapons in certain circumstances, and seven to oppose it. The President - an Algerian judge - has a second, deciding vote and the court's ruling may depend on this.
The official British view, cited by the former Foreign Office legal adviser, Sir Vincent Evans, is that the use of nuclear weapons may or may not be legal depending on the circumstances. However, Sir Vincent has said, the more you examine the circumstances, the more you are driven back to a general principle.
Dame Rosalyn Higgins, the new British judge, said recently: "To my knowledge governments do not at all try to influence the judges in cases before the court in which their national interests are deemed to be at stake. Indeed, it is when a case from one's own country is before the court that the judges are most sensitive to demonstrate their independence."
It is possible the court will fudge the issue by, for example, ruling only that the international laws of armed conflict apply to nuclear weapons. That would satisfy the British, who believe that the legality depends on the circumstances. But such a ruling would do nothing for the image of the World Court.Reuse content