Tens of thousands of drivers are being secretly followed by a network of CCTV cameras on Oxfordshire's roads.

But you are not allowed to know where they are.

Police have 31 fixed Automatic Number Plate Recognition (ANPR) cameras, which collect data on 45,000 cars every week.

Meanwhile, Oxfordshire County Council has 25 ANPR cameras, to track cars' journeys.

The lenses are trained on the roads to gather information on thousands of drivers and create a map of where they go.

Both the council and police have refused to reveal where their camera sites are and will not even reveal what they look like.

However, the Oxford Mail has spotted ANPR cameras in London Road, Headington, and on the Oxford southern bypass at Heyford Hill.

The secrecy about the cameras has been criticised by the AA, as well as civil liberties groups. But Det Supt Richard List, of Thames Valley Police, said: "For operational reasons, we're unwilling to reveal the number of ANPR sites in Oxfordshire.

"Placing this information in the public domain may have a negative impact on our ability to reduce crime and detect criminal offences.

"ANPR is a rapidly developing area of policing and it's important that operational sensitivities are protected.

"This is to the benefit of both ourselves and the local community."

Police authority paperwork shows there are 31 police ANPR cameras, with ANPR access to 27 further CCTV cameras, and a planned network of 66 cameras by the end of the year.

The Oxford Mail has learned police and the county council entered into a verbal agreement last year allowing them to put up as many of the cameras as they want without planning permission or public consultation.

About 1.9 million cars are read by the police cameras every week and police expect that number to grow.

Supt Mick Doyle, the head of roads policing in the Thames Valley, said: "Static cameras are used primarily as an intelligence-gathering tool. When a high-level crime is detected on a camera it is acted upon immediately.

"But vehicles which come into the low-level category (minor driving offences) are logged and the information we gather on them is used to build up a picture of how the vehicle is being used.

"This can then be used at a later date to prosecute motorists driving illegally."

The county council's cainey member for transport, Ian Hudspeth, said he believed the public should know the camera sites.

But council spokesman Paul Smith said it would not release the information, because the public could then identify the secret police cameras.

Mr Hudspeth said: "We track the number plate, not the driver. We do not want to find out what you are doing as an individual, but where the car is going.

"We will certainly not share the information with anyone else. We simply want to see when the journeys start and finish. We do not want personal information.

"An encryption on the camera (to prevent abuse) shows we're not interested in who's driving, but where it's going to and from."

A spokesman for the Association of Chief Police Officers said data on drivers was kept for two years and shared with the Home Office, Department for Transport and the DVLA.

Only authorised police officers are allowed to check the data, the spokesman added.