Hertfordshire Constabulary's use of number-plate recognition technology in the town of Royston has been declared illegal by the Information Commissioner, reports the BBC.
The Information Commissioner's Office has ruled that the use of number-plate recognition technology in and around the town of Royston breaks the law because the police have not conducted the necessary privacy checks on data collected.
The ICO's head of enforcement has spoken out to question why a small town requires 24-hour number-plate monitoring.
Data protection and privacy laws mean that public bodies must be able to justify the collection of personal data as being proportionate to a legitimate aim.
"The use of Automatic Number Plate Recognition (ANPR) cameras and other forms of surveillance must be proportionate to the problem it is trying to address," said Stephen Eckersley of the ICO.
"After detailed inquiries, including consideration of the information Hertfordshire Constabulary provided, we found that this simply wasn't the case in Royston," he added.
The town has seven ANPR cameras, which effectively record the comings and goings of every vehicle into and out of the town.
The ICO has told the police that it must justify the presence of the cameras, or remove them.
In response Hertfordshire Constabulary said that it would not appeal the ruling, but emphasised the importance of ANPR cameras in police work.