An investigation has been launched after a police call centre operator was shot in the chest with a Magnum revolver during a firearms awareness course.

The man, who is in his 50s but has not been identified, remains in a serious but stable condition after being shot at close range in a classroom at police offices in Oxford Spires Business Park in Kidlington on Wednesday.

The sessions are held regularly to teach civilian staff who may come into contact with firearms about weapons and safety.

Sources told The Oxford Times weapons on these courses should never be loaded with live ammunition.

The Independent Police Complaints Commission (IPCC) yesterday launched an investigation into the shooting. Its evidence may be passed to the Crown Prosecution Service for criminal proceedings.

When the injured man was shot in the chest other members of the course rushed to give first aid and keep him alive until paramedics arrived.

It is understood the injured man has been with the force for a couple of months and is on his nine-month probation period.

An experienced police officer said: "I can't see why you would have a loaded gun at one of these sessions.

"The only thing I can think is someone made a mistake and brought something out of the store and it has a live bullet in it.

"There is no way you would load a weapon for support staff. If you have live ammunition it should be on the range. I think it's appalling but mistakes happen."

IPCC spokesman Poppy Turner said a non-Police standard issue revolver has been removed from the site and witness statements, forensics and ballistics studies were under way as part of a criminal investigation.

The Oxford Times understands the gun used was a .44 Magnum revolver and fired by a Home Office trained Thames Valley Police firearms officer.

Police union Unison has asked to see the risk assessment used on the course and whether guns were checked for bullets before being removed from the police armoury.

Rod Matheson, Unison branch secretary for Thames Valley Police, said: "I have been on many of these courses over 25 years and the bullet and the gun should never ever meet.

"It was certainly not a malicious act. It was obviously a genuine accident.

"I have heard stories that two members of staff with first aid were on the scene quickly and helped keep this bloke alive until the ambulance arrived. Without their efforts it would have been a lot worse."

IPCC Commissioner Deborah Glass said: "The investigation will examine how live ammunition came to be present in a firearm during an awareness session, and consider whether any criminal or disciplinary offences have been committed."

The instructor has been moved to non-firearm duty while the investigation is conducted.

Thames Valley Police has only shot and killed one person, Jason Gifford in Aylesbury in 2002.