Leading Article: Swapping Trident for a shield

The world, so the argument goes, is today a more dangerous place than it was during the Cold War. Then two massive nuclear arsenals held each other in calculated paralysis. With mutually assured destruction as the inevitable outcome, the possibility of the weapons being used was remote. By contrast, so we are told, today we are prey to the more real possibility of a strike by nuclear terrorists or some rogue nation with a wild leader.

The truth is that it was always more likely that any nuclear conflict would be started by a reckless superpower proxy; it is widely believed that Israeli technicians began to assemble components of what were then very basic nuclear weapons for a strike on Cairo when Egyptian tanks were racing across the Sinai as long ago as 1967. The real terror was that the superpowers would inevitably be drawn in with weapon stocks whose power was beyond comprehension. It is the decision by the Americans and the Russians, under the Start treaties, to get rid of two-thirds of those missiles that removes what was a threat to the very continuation of the world.

And what of the rest? The Nuclear Non-Proliferation Treaty - which was signed in 1970 and which expires next month unless it is renewed at the review conference that began in New York yesterday - has been a greater success than anyone could have imagined. Predictions that there would by now be 20 or 30 nuclear states have been confounded. Today, in addition to the original five nuclear states (America, Russia, Britain, France and China), there are only a handful of extra nuclear powers : India, Pakistan, Israel and possibly North Korea. Some 175 of the UN's 185 nations have signed up to an agreement that gives them access to nuclear technology for peaceful purposes in return for agreeing not to try to acquire the bomb. The authority of such a treaty resides in its being passed by the biggest majority possible. The problem is that many existing signatories are becoming disgruntled with the tardy progress of the nuclear powers towards speedier disarmament.

To win them round will require significant movement from the main nuclear powers like Britain. Today, the Foreign Secretary, Douglas Hurd, will tell the conference in New York that Britain is ceasing the production of nuclear explosive material and will scrap about 100 nuclear bombs designed to be dropped from aeroplanes. It will be a bit of a con, for Britain has produced very little such material since 1979 because we recycle old warheads; indeed, the free-fall bombs are being scrapped only so that they can be turned into warheads for the Trident missile system now entering service.

There's the rub. Trident, contrary to the trends everywhere else, actually expands our nuclear capacity. The strategists will tell you that it is a "minimum" deterrent and that it is impossible to get any smaller. Such thinking is based on Cold War analysis that is now outdated. Britain should shift its emphasis to ballistic missile defence - shooting down incoming missiles, much as Patriots shot down Scuds in the Gulf war. Such a strategy would have proved useless against a massed onslaught from an arsenal the size of Russia's or America's. But current studies show that it would be an effective method for a small island like Britain to intercept a few missiles from a renegade state.

Building such a system would provide profitable work for many of our defence companies. In the difficult task of turning swords into ploughshares, building shields would be a good beginning. Such a development would enable Britain to place Trident on the negotiating table and to extract concessions from other nuclear powers in return. The time is ripe for such boldness.