Medical organisations tried to defuse growing public fear yesterday over the potential threat of anthrax as a terrorist weapon.

Doctors believe that the panic over anthrax that has gripped America is out of proportion to the threat and could do as much harm as the bacterium itself if it spreads to Britain.

The Royal College of Physicians is planning a meeting within the next week to explain the real risks from the disease, which are lower than widely feared, and the difficulty that any terrorist organisation would encounter in spreading it. Professor Liam Donaldson, the Government's chief medical officer, who has agreed to speak at the meeting, said yesterday that anthrax could not spread from person to person and any outbreak was likely to be localised and manageable. Britain was well prepared to cope with any attack.

"We don't have any evidence that there is any threat or risk but it is our responsibility to plan and that is what we have been doing over the past two weeks," he told the BBC.

"If someone did develop symptoms it would be a result of some sort of exposure ... tied to particular incidents, the opening of suspect parcels and so on. So people would be coming to seek help on the basis of a specific incident, not on the basis of feeling generally unwell," he said.

Experts in biological warfare emphasised that although anthrax is potentially lethal – especially if more than 2,000 spores are inhaled – it is difficult to generate the conditions where more than a handful of people would be at risk.

The biggest known outbreak of pulmonary anthrax occurred in the former Soviet Union in 1979 after an accident at a secret military establishment. About 70 people are known to have died in the incident but several thousand more are thought to have survived the exposure to anthrax spores.

Fanatical followers of the Aum Shinri Kyo cult in Japan tried several times to infect the Japanese underground system with anthrax but failed to cause a single death from the disease.

Professor Alastair Hay, a specialist on biowarfare at Leeds University, said: "Inhalation anthrax is not a significant problem. It must be distributed in a very fine particle spray and that sort of technology is not generally available."

Peter Emmerson, professor of molecular biology at Newcastle University, who is working on new anthrax vaccines, said that the risks should not be overstated.

"It's been blown out of all proportion in the US but you can see how. The Americans have been very fast to close down buildings and test people but this creates its own panic," Professor Emmerson said. "Every crank in America must now be sending out packets of white powder to people they don't like. Only one needs to be genuine to cause a scare," he added.

Anthrax causes three types of disease – pulmonary, intestinal and cutaneous (skin) – depending on the route of entry of the bacterium. Although pulmonary anthrax is the most lethal form, with 90 per cent mortality, all three can be treated successfully with antibiotics if the infection is caught early.

The Bacillus anthracis bacterium is not contagious and an infected person has never passed on the disease to others. Scientists fear, however, that attempts are under way in terrorist circles to generated genetically modified strains of the microbe that are either more virulent or antibiotic resistant.

The British Medical Association said calls from the public asking where they could get anthrax vaccine and gas masks had risen sharply in recent weeks.