A covert network of police cameras secretly tracking driver journeys and number plate details is to be almost doubled.

Police will spend £1.2m on 34 new static automatic number plate recognition (ANPR) cameras — at a cost of £35,000 each — to catch illegal cars and wanted criminals.

The information will be shared with other organisations, but police are keeping their identities a secret.

Human rights campaigners have urged Thames Valley Police to ensure innocent drivers’ details are protected.

The camera, separate to a similar expansion of county council cameras, will be set up over the next three years across Oxfordshire and the Thames Valley.

There are 47 police cameras on CCTV poles and traffic lights.

Thirty-one police vehicles are fitted with the cameras, there are 11 portable kits and one in the force helicopter.

Assistant Chief Constable Nick Gargan would not reveal the locations of ANPR cameras, fearing it would encourage criminals to avoid them.

And police would only provide one example where an ANPR camera was used in securing a criminal conviction.

Mr Gargan said: “For operational reasons, we will not be disclosing the location of ANPR cameras operating in Oxfordshire.

“Thames Valley Police is committed to working in partnership with a variety of other agencies. However, for operational reasons, we are not going to release the names of the organisations to which the information is passed.”

James Welch, legal director at human rights organisation Liberty, said: “While ANPR may have a role to play in the investigation of serious crime, the private information that it gathers should not be bandied around willy-nilly.”

Police would not reveal any examples of Oxfordshire crimes solved due to ANPR.

But Mr Gargan said a police ANPR camera on the M40 in Oxfordshire was used in the investigation and subsequent conviction of the killers of Hell’s Angel Gerry Tobin in Warwickshire two years ago.