Planning for a bioterrorist attack in Britain moved up a gear yesterday as the government issued fresh guidelines to health authorities on how to deal with botulism, bubonic plague and smallpox.

The advice was sent out by the Public Health Laboratory Service, but the government's chief medical officer, Professor Liam Donaldson, insisted there was "no specific threat" to Britain, and urged people not to panic. He said "governments usually concentrated on" the three agents, plus anthrax, when facing a terrorist threat, although there was no current suggestion they might be used.

As false alarms again disrupted services across Britain, Professor Donaldson condemned hoaxers who spread panic and put extra pressure on emergency services. He asked the media not to exacerbate fears. "It isn't right that people should be alarmed and there is no need for it," he said.

The Government faced a dilemma because it had to plan for any possible attack but, in making the plans public, it increased fear among the population. Professor Donaldson said: "If it is bioterrorism that is behind these [US anthrax attacks], it is the fear they are producing that is bringing the success they are achieving.''

Smallpox would potentially pose a bigger threat, because it is contagious and can spread through the population. However, only two samples of the virus are held, in laboratories in the US and Russia, and terrorists are not thought to have access to either.

Botulism is a food poisoning bacterium and one of the most lethal toxins known, but it would be even more difficult to distribute than anthrax. Bubonic plague, a form of which was responsible for the Black Death pandemic in Europe and Asia in the 14th century, responds to treatment with antibiotics.