Records retained in departments, if selected for permanent preservation, are listed in the National Archives catalogue and are subject to the provisions of the Public Records Act. According to the National Archives Catalogue there are 22,318 files retained in departments that are over 30 years old.
Retained records are still subject to the Freedom of Information Act. It is not possible therefore to identify how many are unavailable to the public, but members of the public may make a request to have the file made available under the Freedom of Information Act. Records are listed in the catalogue by their creating body (not that which currently has custody) and machinery of government changes over time mean it is not possible to provide a detailed breakdown by department.