Why old personal and intelligence files stay closed

Why might old personal or intelligence files remain closed long after the war?

They may protect living people, sit under separate Royal Archives custody, or reveal intelligence sources and methods that still have security value.

Prince Philip's personal papers are likely to be held in the Royal Archives rather than released on an automatic timetable. Some closures protect people from renewed scrutiny while they are still alive. Other files contain signals-intelligence sources or analytical methods that remain relevant to current work. The age of an operation does not by itself remove every privacy or security reason for withholding its records.