The Times reported prison authorities suspect that the leak may be linked to organised crime groups aiming to use drones to smuggle drug into prisons, while the blueprints could be used to evade security measures.
The leaked blueprints are reported to include the locations of key security features, such as cameras and sensors, making it easier for criminals to bypass security or exploit vulnerabilities.
It is not clear which prison plans were affected.
The Cabinet Office and the Prison Service are said to be working to identify the source of the breach and assess who might benefit from the information.
The National Crime Agency told the it was providing support in an advisory capacity, but it would be “incorrect” to say it was investigating the incident.
A MoJ spokesman said: “We are not going to comment on the specific detail of security matters of this kind, but we are aware of a breach of data to the prison estate and like with all potential breaches have taken immediate action to ensure prisons remain secure.”
The leak was first flagged in an internal alert issued earlier this month, seen by the paper.
