Charles Clarke, the Home Secretary, yesterday set out a list of “unaccept-able behaviours” that would allow for the exclusion and deportation of foreign extremists from this country. The behaviour includes the formentation, justification or glorification of terrorist violence; writing, producing, publishing and distributing material likely to promote terrorism; and running a website which would have the same effect. His plans were, understandably, well received by the two opposition parties.

They may, though, be greeted with a weary sigh by those who have had to confront domestic terrorists and terrorism in a different context. The closure of Darley Oaks Farm in Newchurch, Staffordshire, followed a six-year campaign of intimidation against its owners, including a sickening act of grave-robbery. It is another small victory for a band of fanatics who have made life for companies who have any link with animal experimentation, and their employees and suppliers, increasingly insuffer-able. In a noble attempt to confront this trend, the Research Defence Society yesterday released a declaration of support for this research from more than 500 leading British scientists.

In theory, the law should now make the prosecution of these zealots much easier. The Serious Organised Crime and Disorder Act, which came into effect on July 1, introduced a new offence of “economic sabotage”. This is designed to ensure that so-called animal rights activists who seek to force research organisations out of business can be imprisoned for up to five years. This represents a considerable toughening of sentences which, on the regrettably relatively rare occasion of a conviction, have often been for no more than three months behind bars.

As a declaration of principle, this legislation is admirable, even if perhaps a belated response to a menace that has been evident for the better part of a decade. Whether it will make the difference it should is, however, debatable. For as we report today, legal advisers to companies that have suffered harassment believe that proving an intention to commit economic sabotage will be very difficult and that even if alternative legal avenues could be explored — such as conspiracy to commit a public nuisance — the letter of the law is only as effective as the energy which the police put into tracking down these highly committed criminals. This, unfortunately, is in doubt.

While the possibility of serious punishment remains contestable and the commitment of the authorities is considered vague, there is little reason to think this form of terrorism will disappear. It is more likely that other small and large companies, and parti-cularly the universities, will reluctantly conclude this is work that is more trouble than it is worth. This will be even though, as the Research Defence Society observes, a “small but vital part” of the research that has transformed medicine involves animals.

This would be a tragedy for human wellbeing as well as a sharp economic blow to the £3 billion-a-year life scien-ces industry. Its perverse impact would be to shift this research to nations where the controls on animal experimentation are not as comprehensive or constrictive as in this country. The broader lesson for the Home Office, nonetheless, whether it refers to animal rights dogmatists or al-Qaeda sympathisers, is that stronger laws or extra powers, while useful, are not the end of the matter. Extremists must believe that they will be implemented.