"From a policing point of view, a society which is itself unarmed and has an unarmed police force is the ideal," says Mr Alderson.

"We only have to go to America to see that where everybody is entitled to have a gun and the police are not only shot at, but they also shoot each other in shoot-outs from time to time.

"That is the kind of situation that we have always looked down upon as being unwise. But you can't expect officers to go out on the streets of this country into armed situations and not be armed themselves."

Mr Alderson believes that if more criminals carry guns and are prepared to use them, then the police have no option but to respond.

"At the end of the day if you are facing armed terrorists, you can't say, 'Excuse me chaps, you should put those guns down' - you have got to be able to respond in kind."

He says that there could come a day when British police carry guns as a matter of course.

"I think again a policeman cannot do his job without the tools and if it is more often than not that firearms are likely to appear in incidents then you are getting near to the stage where policemen have to be armed as a routine measure in most cases," he says.

Keeping the public informed

"It is no good going to a situation where members of the public are being threatened or shot at... and all you can do is hide behind a wall because you haven't got the means of defending these people."

He believes it is crucial to keep the public was kept well-informed about any decisions regarding the arming of police.

"If it came to it that the chief constables collectively thought that they would have to take this move, and if the home secretary thought they would have to make this move, it would be very, very important to inform the public in advance and to educate them and to give information and to show them what the statistics were and what the risks were and so on," he says.

"It is not just a question of arming the police because it is a good gesture to serve notice on the criminals, it is more than that. It is a change of culture in our country that we would be unlikely ever to reverse, I think.

"I have always believed that the police and the public are in a contractual relationship with each other and in a contract you have got to have both parties more or less agreeing with what you propose to do. So a big change in police culture like this should morally take the public along with it.

"So they would have to be informed about it, MPs would have to talk to their constituents and explain why this is taking place, the press and the media generally would have to play a big part in this and it would be a big step."

Culture of firearms

Mr Alderson says the cultural change involved in arming police would have a big psychological effect on the British public and police alike.

"I was a soldier before I was a policeman and if you are walking around with a gun on you it gives you a feeling of omnipotence almost - that you can get away with stuff that you couldn't get away with if you didn't have a gun. In other words, a gun affects your mentality and that would have to be guarded against in my view. The police themselves would have to be trained about the whole question of the culture of firearms."