Urgent action has been taken to secure prisons in England and Wales after it emerged that blueprints of jails had been leaked online.
The Ministry of Justice said immediate steps had been put in place in the wake of the major security breach.
There are fears organised crime groups could use the information to plan escapes or smuggle drugs or weapons to prisoners.
Last year former soldier Daniel Khalife escaped from HMP Wandsworth and spent four days on the run.
The 23-year-old slipped out of the jail by clinging to the bottom of a food catering truck using a sling made from kitchen trousers, triggering a major manhunt which saw him arrested on a canal towpath next to the Thames.
The blueprints were said to include the locations of cameras and sensors, a key security precaution in jails.
Officials are now working to identify the source of the leak.
Ian Acheson, a former prison governor, told The Times that organised crime groups could use copies of the layouts along with other public information.
He said: “If plans of high-security prisons have been leaked, coordinating that with open source material or Google maps could aid an escape after an attack on the exterior of the prison. Much more plausible is using additional data to coordinate drone drops. But if you can deliver half a kilo of drugs via a drone then you can deliver weapons, explosives, whatever you want. These places are wide open.”
He added: “The dark web is a marketplace for criminals and terrorists. Detailed maps of our most secure institutions which hold enormous national security and organised crime risk should never end up as commodities for sale online.”
He called the breach a “very serious breach of IT security” and called for a wide-ranging and independent investigation into how the plans were leaked.
A Ministry of Justice 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.”
Last month, police warned that gangs were recruiting skilled drone pilots to fly drugs to prisoners’ cell windows.
The machines were capable of flying “huge payloads” of up to 7kg, in highly accurate deliveries, they said.
