This is one of four dilemmas that could happen on a typical call-out, says a Cheshire police firearms officer.

Maybe, he says, if he doesn't fire and he is lucky, the suspect's gun will turn out to be an imitation.

But the officer said: "If I fire and I have made the wrong decision, I will go to prison.

"Or if I fire and I get it right, I still get suspended while an inquiry takes place, putting me and my family under a great deal of stress."

Armed police hit the headlines earlier this month after an inquest jury returned a verdict of unlawful killing on the shooting of Harry Stanley, a 46-year-old father-of-three.

Mr Stanley, a Scotsman living in London, was shot in the street after a shouted warning.

The police had been told an Irishman had left a pub armed with a shotgun - Mr Stanley was actually carrying a table leg.

The two officers involved were suspended after the jury's verdict and more than 120 armed police refused to carry guns for several days afterwards in protest.

The campaign group Inquest wants the two officers involved prosecuted for manslaughter.

Cheshire police's chief constable Peter Fahy said: "There is no question that firearms officers must be accountable under the law, the same as members of the public.

"At the same time, the criminal justice system needs to recognise the unique position firearms officers are in and the split second decisions they have to make.

"The officers involved in the shooting of Harry Stanley have been under investigation for five years.

"That is not fair to them or to the family of Mr Stanley."

Armed police have been patrolling round the clock in Cheshire since 1995, and in 6,500 incidents and 800 arrests not a single shot has been fired at the public.

On call outs they constantly have to decide if someone has a harmless imitation weapon or a deadly firearm.

Of the 24 incidents from April to September where firing weapons caused injury in Cheshire, 24 of these were airguns and BB weapons - only one was a handgun.