The devices enable officers to confront offenders with their crimes by replaying footage to them on the spot. In pilot schemes, offenders have proved far more likely to plead guilty or accept on-the-spot fines or cautions than contest their cases in court.

The Home Office plans a national trial of the cameras using hundreds of officers to assess whether they can increase conviction rates, and they could become standard kit for every police force. They may also help cut crime by, for example, deterring thugs from fighting when there is an officer nearby.

At least 12 offenders have been punished using evidence recorded by the camera — known as the Cylon body-worn surveillance system — since it became available for individual forces to test last December.

The crimes recorded range from breaking into a car to assaulting a police officer and fighting outside a nightclub. After playing back the footage, police say all the offenders accepted their guilt rather than tying up magistrates’ time with a “not guilty” plea.

“We have been getting really good quality primary evidence from the outset and we have had a number of incidents where the offenders have seen the footage and have said ‘Okay, hands up, I cannot deny that’,” said Sergeant Olly Taylor, a beat officer in Plymouth.

After a small-scale trial using 10 cameras, Taylor said he had been asked by the Home Office to conduct a six-month trial starting this September with 200 officers trained to use 50 cameras during day and night patrols in Plymouth city centre.

“We think it can make a real difference in the way we gather evidence in crimes such as alcohol-related violence and yobbery in public places,” he said.

If the scheme is successful, the Home Office will produce national guidelines for all forces with the Association of Chief Police Officers and the Crown Prosecution Service.

Martin Goodall, a chief inspector from Hampshire police, heading the programme for the policing standards unit at the Home Office, said his group would use the trials in Plymouth and in forces including West Midlands, Avon and Somerset and Northumbria to evaluate the camera’s effectiveness.

Each device weighs about 25oz and can produce high-quality digital video or stills and record sound. The camera can be attached to existing police helmets and is worn level with the eyes. It is able to film in whichever direction the officer’s head is turned. A wire links the camera, which is the size of a marker pen, to a 4in screen worn on the belt on which footage can be played.

The device can record 400 hours of footage but must be recharged every 12 hours. The film can be downloaded on to a computer or on to a DVD for use in court.

Each camera costs £1,700 and is made by a Plymouth company called Audax. Steve Rogers, chief executive of Audax, said it had sold about 500 cameras to the 43 police forces in England and Wales.

In March Fiona Linehan, 22, from Plymouth, became the first person in the country to be convicted using evidence recorded by a head camera after assaulting a police officer who was wearing one.

In Benwell, Newcastle upon Tyne, an officer used evidence recorded on his head camera to charge a man after spotting him trying to break into a car in May. “The camera caught him and it was easier to admit guilt than dispute it because it is all on film,” said Sergeant Paul Hamilton, a community sergeant with Northumbria police.

He added: “It is a very good tool. If you are accusing someone of a crime they will plead guilty, which reduces the officer’s time completing files for the court and having to attend court to give evidence.”

Other forces in the trial include West Yorkshire and the Metropolitan police, where four head cameras are being tested by mounted officers in Hammersmith, west London.

The Home Office confirmed it was helping to fund the trial but said the cameras would have to be “independently evaluated” before any nationwide scheme took place.

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