Leading Article: Warning: police road-block

THE Christmas traffic in London is already so bad that it cannot be made much worse by the addition of police road-blocks designed to catch IRA terrorists. A driver who is stationary anyway may just as well while away the time being searched by the police. Yet, although the police are responding to public concern, the operation straddles the borderline of credibility.

A reasonable case can be made for random temporary road-blocks. First, there is always a small chance that one of them will catch a terrorist, since they are set up very rapidly in places that are difficult to circumvent. Second, even if they do not catch anyone, they will make life more difficult for the IRA. Instead of being able to drive freely into central London or Manchester with a van full of explosive fertiliser, the terrorists will be forced to change their plans. They may, for instance, divert to other targets, or switch to less bulky Semtex, which can be carried in the boot of a car, or simply send scout cars to reconnoitre the route ahead. Whatever their response, they will suffer inconvenience.

Third, the public will be reassured by visible evidence that the police are doing something to protect them, which seems to be one of the principal reasons for the operation. Fourth, the public will become more aware of the threat and therefore more likely to supply information leading to an arrest.

The case against the operation can be made with two main points. First, for the reasons already given, road-blocks are very unlikely to catch terrorists. Even in Belfast, where every access route is controlled, bombs still get through. In a city the size of London it is impossible to control more than a tiny fraction of the streets, so the chances of catching or deterring a bomber are small. The best weapon against terrorism is good intelligence. That is where effort should be concentrated.

Second, there is an incipient threat to civil liberties. Police have the power to stop and search under the Police and Criminal Evidence Act of 1984, but they are supposed to have 'reasonable grounds for suspicion that articles unlawfully obtained or possessed are being carried'. These grounds should be specific. Where searches are randomly sited, or applied to vehicles of a particular type, the Act has to be very generously interpreted to cover them.

Moreover, experience suggests that temporary measures can too easily become permanent, that the law, once stretched, is liable to remain that way, and that when the police gain extra powers they will cling to them. The power to stop and search cars without specific grounds can be useful in other areas of crime prevention and is open to abuse.

Given the nature of the threat, the evidence of overwhelming public support for special measures, and the assurance that these will be temporary, few people are going to raise serious objections to the road-blocks. Anything that inhibits or complicates the work of the IRA is welcome. But it is not too soon to raise a small warning flag.

Doubts will be put aside if the road-blocks can be shown to be effective. Since proof is likely to be elusive, the next best answer is to ensure that the road-blocks are, as promised, temporary. Every surrender of what passes for normal life is a victory for the IRA in its campaign to make London more like Ulster.