Mary Dejevsky: So what exactly is the British nuclear deterrent supposed to protect us against?

What should Britain's defence priorities be? What contingencies should we anticipate in the years ahead? By coincidence, the past two days have offered a whirlwind tour of some of the options. The mismatch between threats, structures and funds has rarely been more glaring.

There was a delightfully retro feel around Westminster this past Tuesday evening. Old-style protesters of the hirsute variety sauntered away from their demonstration, brandishing placards in black and white, saying "No" to Trident. They had lost the vote, of course - or rather Tony Blair, Gordon Brown and the Conservatives had won it - but the moral victory, as it always used to be on such occasions, was theirs. This was a good old-fashioned back-bench revolt.

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Within hours of Parliament approving the renewal of a nuclear weapons system designed to counter the superannuated threat from the Soviet Union, yesterday's morning news brought a reminder of quite a different threat to our security. Khalid Sheikh Mohammed, the alleged mastermind of the September 11 attacks on the World Trade Center and the Pentagon six years ago, had admitted involvement in another 30 terrorist conspiracies.

Some of them - the bomb attacks in Bali and Kenya - had taken place to deadly effect. Others (the shoe-bomber) had been thwarted; yet others, including assaults on certain select London landmarks, had thankfully remained a mere glint in his eye. True or not - and there must be considerable doubt about the circumstances and soundness of this supposed confession - the targets would surely feature on any terrorist wish-list.

Then, before these graphic premonitions of multiple 9/11s could quite fade from view, on to our television screens came the Prime Minister, defending the invasion of Iraq four years on. The violence gripping the country, he insisted, was the work of a few extremists. We (presumably he) had brought democracy to Iraq. We (he) had nothing to apologise for. "If we carry on apologising for ourselves, leaving them the excuse that it's because of George Bush that they're doing these terrible things ... the less chance we have of protecting our security." In other words, as Mr Bush has often said, security over there translates into security over here.

What we have here are three snapshots of British security concerns. There is unrest abroad that might be seen as a threat to our peace and quiet at home (Afghanistan and Iraq). There are bands of dedicated murderers and self-publicists, who target national morale as much as life and limb (al-Qa'ida, home-grown terrorists and others). And there is the conventional threat from a big power armed with missiles. Yet the planning and funding seem in inverse proportion to the reality of the threat.

Thus our troops in Afghanistan and Iraq - leave aside whether they should be there, and how far their presence might be aggravating any threat - complain that their numbers, equipment and medical treatment have all been skimped. This is despite the fact that a solid conventional military operation is precisely the sort of thing this country has traditionally excelled at.

Thus the civilian budget has been distorted, though nothing like as much as in the United States, to fight a terrorist threat that is essentially small-scale and haphazard. Israeli-style airport security checks and better internal communications might have prevented 9/11. As for Britain, control orders, around-the-clock surveillance and the introduction of ID cards are extravagances at a time when we have no formal controls on who leaves the country and local constabularies police our borders. If we are serious about national security, the frontiers are surely a good place to start.

And then, of course, there is Trident. How come our most generously funded and longest-term defence commitment is to a project that confines us to a 60-year-old alliance and is geared to combating a threat that no longer exists? How come this most long-term of our security undertakings is the one to be rushed through? If there is one assumption that is a fairly safe bet, it is that Russia will never present a Soviet-style threat. A second, similarly safe bet would be that, even if missiles carrying nuclear warheads remain a favoured weapon into the future, any new enemy is likely to be beyond the reach of our missiles.

Forecasting is a dangerous occupation. But one of the ways in which futurologists have most often erred is in overestimating the pace of change and underestimating how much remains the same. Take just three examples.

First, technology. Even well-funded military research and development tends to advance more slowly than we civilians may appreciate. The most sophisticated devices may have quite limited applications. Even today, most conflicts are fought with conventional tactics and conventional weapons. The Pentagon's lighter, nimbler force was unable to subdue Iraq; the US military was forced back to basics. As for those nuclear missiles: a nuclear capability is a deterrent, not a weapon. One of the most significant recent innovations has been remote-controlled surveillance and weapons that keep humans out of battle.

Second, terrorism. The terrorist threat did not come out of nowhere on 11 September 2001. It had precedents that went back to Sarajevo 1914 in recent history and centuries before that. Memories are short indeed if we forget the Sixties and Seventies, with their PLO hijackings, German and Italian domestic terrorism, and Irish terrorism closer to home. Were they really so different, in terms of causes (and remedies) from what we face now? There are measures and precautions that can be taken. They include not panicking the population or exaggerating the threat, but they are not foolproof.

Finally, co-operation. Alliances and joint capabilities make as much sense now as they ever did. Perversely, political geography has recently changed faster and less predictably than either military technology or the nature of the threat. Few foresaw the collapse of the Soviet Union until the year before it happened, but to preserve alliances and collaborative projects from that era is to fly in the face of the new reality. Meanwhile growth in commercial and demographic power is likely to fuel concern for security, however much the leaders of China - or indeed the European Union - might insist to the contrary.

The top brass and their political masters can be forgiven for craving the familiarity of old alliances and the prestige that is associated with high-tech innovation. From the Trident vote to Mr Blair's remarks on Iraq's security, however, this week has only shown how out of kilter our defence aspirations and capabilities have become. It is time to take a fresh look at the real world around and consider how Britain fits in.

m.dejevsky@independent.co.uk

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