The disturbances would erupt as terrified members of the public became desperate to enter decontamination units provided by the fire service. Inside the units the public would be expected to strip, shower and then dry themselves and put on clean clothes, according to national guidance published by the Home Office yesterday.

It gave warning of the risks to emergency services dealing with a chemical, biological, radiological or nuclear attack. They include harm from secondary devices and ?confused, violent or rowdy victims?, plus undetected perpetrators trying to escape.

?In the case of mass decontamination, and if there is impatience to enter the decontamination facility, respondents should expect public disorder,? the guidance says. The Department of Health has developed a stock of emergency kit for ?rapid deployment in major incidents?.

Part of this has been divided into containers or ?pods? designed to treat 100 people, the guidance stated.

Different pods include nerve-agent antidote pods, several biological ones and equipment pods containing medical equipment such as resuscitation and ventilation kits.

There are also ?modesty pods? containing paper suits, paper towels and silver-foil ?space blankets? for victims who have been decontaminated. Part of the stock has been sent to ?strategic sites? throughout the country with the rest held centrally.

John Denham, the Home Office Minister with responsibility for co-ordinating plans to deal with an attack, said: ?This guidance does not signal a new threat to the UK. If a specific threat becomes apparent, the Government and appropriate authorities will, without hesitation, inform the public of what action to take.?

The guidelines, bringing together existing guidance provided to emergency services, local councils and the health service, point out that a large area might be affected by an attack: ?The amount of damage resulting from a major incident or series of incidents could far exceed the levels of damage produced in previous disasters.

?The numbers of people exposed and requiring decontamination from chemical or biological terrorism may grow swiftly to many more than anything experienced or planned for following conventional disaster or naturally occurring outbreak.?

The 38-page document also said that in the event of a chemical, biological, radiological or nuclear attack, the public may not automatically realise they were involved in a serious emergency.

?It is likely that a terrorist attack would involve a specific target such as a VIP, critical or iconic location, or high-profile event,? the document said. It also said that the public may not display any symptoms for hours or even days following a sudden biological, radioactive, or chemical attack.

The guidance draws together planning done by the different emergency services.