Since the events in the US, we have asked the NHS to review contingency planning arrangements

Alan Milburn, Health Secretary

His comments came after the World Health Organization (WHO) warned against underestimating the risks of possible biological or chemical attacks.

The WHO has issued a draft report advising governments to start preparing response plans in the event of such an attack, which it said could involve diseases such as anthrax, botulism - which causes paralysis - or smallpox.

It has been reported that the NHS is buying decontamination and protective suits on an "unprecedented scale", before the attacks on America.

Anthrax vaccine

The UK is also home to the only laboratory in the world that can manufacture a licensed vaccine against anthrax.

The Centre for Applied Microbiology and Research, based at Porton Down in Salisbury has produced tens of thousands of doses of the vaccine.

Before the attacks, the Ministry of Defence had decided to make the anthrax vaccine available under a voluntary scheme to troops going to the Gulf, or other areas where there is a risk of anthrax being used as a biological weapon

Health experts in the UK have been planning how to react to a bio-terrorism attack for several years.

The Sarin nerve gas attack on Tokyo's underground which killed 12 and left 1,000s sick in March 1995 awoke governments to the risk of bio-terrorism attacks on cities.

Deadly diseases which could be used by bio-terrorists include anthrax, smallpox, yellow fever, forms of Ebola and botulism.

Small quantities can be deadly, and they can be delivered by air, possibly using some form of aerosol.

Preparations

Dr Nigel Lightfoot, group director of the Public Health Laboratory Service (PHLS) in the north, told BBC News Online: "We have been working with several government departments for the last few years, but its always been done quietly in this country because they don't want to attract attention."

The attacks on America have drawn public attention to what plans might be in place.

He added: "We hope that any bio-terrorist attack would be recognised very early."

Dr Lightfoot said there was a communication system established so key people would be informed of any attack, and what the substance was.

The PHLS has 49 laboratories around the UK which would provide information about the outbreak.

They, and specialist reference laboratories at PHLS headquarters would be able to offer advice to NHS workers who may have to deal with victims of the attack.

He said: "These laboratories and specialist reference laboratories at the PHLS headquarters in North London would provide diagnostic experts for these unusual substances.

"Clinical experts in these areas would be available who are able to give advice."