Figures released under the Freedom of Information Act have revealed that 233 million vehicle number plate checks were made under Sussex's Automatic Number Plate Recognition (ANPR) system last year.

Vehicles being driven without tax or insurance or linked to someone suspected of a crime accounted for six million of these hits.

So is the ANPR system affecting our civil liberties or helping to remove more criminals from the streets? Ruth Lumley reports.

John and Linda Catt know more than most what it is like to be under surveillance.

The father and daughter are peaceful protesters who exercise their right to demonstrate their opinions in a way they see fit.

They have never been arrested, neither has a criminal record, and Miss Catt is a 49- year-old lawyer.

Yet they say they have become the victims of a “police state” after a marker was placed against their car on the Police National Computer by Sussex Police because they had attended three demonstrations against EDO MBM in Moulsecoomb, Brighton.

Months later, an ANPR camera in Central London flagged them up as “of interest to the public order unit in Sussex”.

They were pulled over and searched by a police antiterrorism unit – and threatened with arrest under the Terrorism Act if they did not explain where they were going.

Implicated Mr Catt, 84, and his daughter say surveillance, coupled with anti-terror powers, means innocent people are criminalised merely for appearing on police databases.

ANPR cameras read number plates and record the time and date where a vehicle has been spotted.

They are chiefly used to track cars which have been reported stolen or are suspected of being linked to a crime.

Their use has become widespread and a project is under way to create a central national database and adapt thousands of CCTV cameras to use the technology.

Sussex Police alone records up to 1.2 million car journeys a day using ANPR and regards it as a vital tool in fighting crime.

Digital images are captured through using the ANPR cameras in either mobile units or at fixed sites, including motorway bridges.

Sussex Police have said that all images which are recorded are automatically encrypted, numbered and then stored on secure computer databases.

The system is able to cross reference data against the Police National Computer and the DVLA database and highlights vehicles of interest to the police so officers can track them.

Sussex Police has refused to confirm or deny whether the police marker still exists against the Catts’ vehicle and Miss Catt has made a formal complaint to Sussex Police about them being stopped in July 2005.

Their complaint was not upheld by the Independent Police Complaints Commission or the City of London Police.

They were told the use of the marker was “proportionate and appropriate”.

Miss Catt and her father say the use of the police marker has been used against them for simply exercising their democratic right to protest against the multibillion-pounds arms trade.

She wants to see the ANPR system regulated so innocent people are not targeted.

Civil right groups are also firmly in that camp.

Liberty, which campaigns for human rights, has said the case is an example of an apparent misuse of Section 44 of the Terrorism Act and that this type of response to lawful protest fails to respect privacy rights and only helps to undermine public trust in the police.

Paul Mackie, compliance director of CameraWatch, a not-for-profit advisory body said that at the moment 90% of CCTV systems do not comply with the law.

He said: “Certainly ANPR is a form of surveillance.

“One of the fundamental points of cameras under data protection is that it covers CCTV and surveillance.

“One of the concerning issues, particularly on garage forecourts for example, where ANPR is in operation, is that a camera could be sited high up on a wall or on a roof, so it would not just be picking up people’s number plates but also their personal images.

Their image is covered by data protection.

“If a staff member leaves work early and is caught on CCTV, would the boss be able to use the footage to reprimand the employee? “There is a big issue of overuse, misuse and the abuse of CCTV which could happen.”

CameraWatch is hoping that the Information Commission will gain more powers so the way CCTV is used can be further regulated.

But Inspector Mark Clothier, from Sussex Police Road Policing Unit, said: “It is an excellent bit of kit.

“They identify vehicles on the road which are not taxed or insured and those who are driving without a licence.

“If your car is stolen it will be easier for us to trace.

It allows us to target suspects using criminal intelligence.

“If you are a law-abiding user of the road you have got absolutely nothing to worry about.”