The Information Commissioner's Office (ICO) has upheld a decision by the BBC to keep details on TV detection devices private.
The ICO agreed with the BBC that disclosing the information could assist people who wish to avoid paying the licence fee.
In 1991, the BBC became the statutory authority for the television licensing regime. As part of its enforcement activity to ensure people pay their licence fee, the BBC relies on a number of deterrents.
Television detection equipment is used to provide final confirmation of suspected TV licence evaders. A complainant under the Freedom of Information Act requested information from the BBC relating to the number of TV detection devices, how often they are deployed and their technical specification.
The Assistant Information Commissioner Anne Jones considered the BBC's argument that it relies on the threat that vans could be used at any time to catch evaders.
This "understanding is maintained", it said, by ensuring that the number of detector vans in operation and the location of their deployment is not common knowledge.
The BBC said that releasing the information "would damage the public's perception of the effectiveness of TV detection vans". The Assistant Information Commissioner agreed with the BBC, that if the deterrent effect were lost, some people would not pay their licence fee.
The BBC also maintained that details of the technical equipment used in the vans must not be revealed, because it would allow people to analyse them and find weaknesses to evade detection.
The Assistant Information Commissioner went on to consider the public interest in disclosing the requested information. In her view, not releasing the information was in the public interest for legitimate licence fee payers.
This was because it helps the BBC keep the cost of enforcement activities to a minimum, allowing money received from TV licensing to be spent on programming.
She concluded that the public interest in maintaining the exemption outweighs the public interest in disclosure, and that no further action is required by the BBC.