By Sally Chidzoy
Home affairs correspondent, BBC East
Standford Hill prison was sent the books earlier this month
The security of magistrates across Norfolk has been compromised after their personal contact details were mistakenly sent to a prison.
The BBC has learned the magistrates' year book, containing names and phone numbers, was accidentally sent for printing to HMP Standford Hill in Kent.
Her Majesty's Courts Service's area director has written to all magistrates to say he is "desperately sorry".
Hard copies of the document at the prison have now been destroyed.
Security procedures have been tightened to ensure the mistake did not happen again, a spokesman for HMCS said.
The details in the book do not include addresses.
The Category D prison, in Sheerness, has had the books since the beginning of January, but the mistake has only just been discovered.
Paul Allen is chairman of the Norwich magistrates' bench
One magistrate from Norfolk said that many of his colleagues would be concerned by what had happened.
"It doesn't particularly concern me as anyone can look in the phone book and find my name, but some magistrates could be really worried - there will be those who will be terrified," he said.
It is understood that the printing of magistrates' year books is usually undertaken at a "more secure" printers.
A HMCS spokesperson said: "HMP Standford Hill is a Category D prison and the workshop, which is supervised at all times, is staffed by prisoners assessed as low risk.
"All hard copies and electronic copies of the document at the prison have now been destroyed.
"The screening process for documents to be printed at the prison workshop has been made more secure to ensure this does not happen again."