Thousands of precious Ministry of Defence (MOD) documents have been sealed due to asbestos contamination.
The MOD discovered that the archives containing all of its most highly sensitive files are contaminated by asbestos, said a report.
The files include documents relating to British nuclear policy and defence and intelligence assessments throughout the cold war.
The files had been stored in the basement of the Old War Office in Whitehall. The report said the files had now been removed to a site on the edge of London.
Some of the affected files had been selected for release at the National Archives in Kew. The MOD said the documents would now be ‘safeguarded' until an assessment is made on how to make the files safe to access.
