There have been major security alerts

Civilians caught in a chemical, biological or nuclear strike area could face "unsavoury" action as police battle to maintain order, officers' representatives have warned.

The Police Federation annual conference in Blackpool was told "very unsavoury, but necessary" action could be needed to control crowds because of a shortage of officers trained to deal with an unconventional attack.

Bob Elder, chairman of the constables' central committee, said the government had not made clear how important it would be to keep the public inside a cordon after an attack.

"This is not about creating mass hysteria," he said.

"This is about the opposite. The public has a right to know."

[People] may be forced to remain in an infected area so as to ensure containment Bob Elder Police Federation

He added: "The natural reaction from the public caught up in such an incident will be to get as far away from the scene as possible.

"This could, of course, only extend the problem.

"There may well have to be some very unsavoury but necessary decisions taken in controlling an infected area."

He said people needed to be made aware of what could happen in the event of an unconventional attack.

"A public information film should be available for regular broadcast to ensure the public know and understand what to expect.

"They must understand that in the event of such a terrible incident they may be forced to remain in an infected area so as to ensure containment."

But he said the shortage of specialist officers would exacerbate the measures needed to maintain a cordon in an inner city area to prevent contamination being spread.

"The first information that we are likely to know that a chemical or biological attack has happened is when the emergency 999 calls come in to say, for example, that people are collapsing in King's Cross station or Birmingham New Street or wherever.

"Only those properly trained and equipped will go, but do we really have enough of those officers? No."

Home Office officials have said in the event of an attack, the area immediately surrounding the scene, known as the "hot zone", would have an inner and outer cordon, with mobile shower units.

Thousands trained

Police would stop anyone leaving the hot zone until they had stripped and been decontaminated.

A Home Office spokesman said there were more than 2,350 officers trained and equipped for all unconventional attacks, with another 3,400 trained to use chemical suits.

But he said the government did not believe a public information film would help.

He added: "Police have the right to detain people under normal powers if they present a risk to the public.

"There are no circumstances in which police could operate some kind of shoot to kill policy under the law.

"There could be no circumstances of 'martial law' which could override, for example, the European Convention on Human Rights."