NHS hospitals and health authorities have been warned to make emergency plans in case of a biological weapon attack by terrorists. The threat of an attack has been described by the British Medical Association as "at an all time high".

Guidance to all NHS trusts, ambulance services and directors of public health was issued last month.

Police teams trained by scientists from Porton Down, the Government's research centre on biological and chemical warfare, would take a lead role in the event of an attack. Joint Health Advisory Cells, combining local police and medical authorities, would be established. A Health Department spokesman said: "The purpose is to enhance our ability to respond to an attack, although there is no suggestion any group is planning one."

The head of health policy and research at the British Medical Association, Professor Vivienne Nathanson, said biological weapons had been more difficult to produce than chemical weapons, but that was changing. "The level of risk is at an all time high because the technology is making it easier," she said.

In February, Donna Shalala, the US Secretary of Health and Human Services, called for the stockpiling of drugs and vaccines and urged public health officials to prepare for a criminal or terrorist attack involving biological weapons.

Sarin nerve gas was used in an attack by a Japanese terrorist organisation five years ago, in which 12 people were killed and 5,000 injured. In the US, the potentially catastrophic consequences of an attack using anthrax or the smallpox virus has led President Clinton to raise the bio-terrorism budget from $158m last year to $230m this year.

In the UK, the likelihood of an attack is considered low by the Health Department.

Britain was approaching the problem in a quiet manner, in contrast to the US, which had been subject to a spate of hoaxes, according to an article in the current issue of the journal of the Association of Clinical Pathologists. One of its authors, Dr Nigel Lightfoot, director of the Public Health Laboratory Service in Newcastle, said Britain had the best system of surveillance in the world with its network of public health laboratories.