This series contains registered files in the 'subject' series. It comprises material relating to substantive subjects and items within the scope of the Cabinet and its committees, together with a variety of matters dealt with or referred to the Cabinet Office.
Piece numbers 161 to 299 are not used.
In January 1966 the Cabinet Office introduced a new filing system in the registry which served the Cabinet Secretariat. Files were of two types; the Subject series and the Committee series. The Subject series, which was much larger, was based on a 'theme' system, whereby file series were created using a theme or a combination of themes. They were numbered sequentially so that there was no connection between adjacent series, e.g. 154 could be NATO and 155 could be Water Supplies. (This differed from the former system with its pre-existing numerical hierarchy into which new files were fitted and where adjacent numbers were closely related.) Individual files created in each series were given numbers separated by a stroke from the series number e.g. 120/3 is the third file in series 120. No further sub-numbers were used, which again had the effect of separating closely related files.
The theme system continued until 1992.
Some pieces in this series originally contained NATO documents, which were extracted and replaced with dummy cards when the pieces were transferred to the PRO. The dummy cards state that the extracted documents are retained by the Cabinet Office. With the agreement of the PRO, these extracted NATO documents were destroyed by the Cabinet Office in May 2001. Researchers wishing to seek access to extracted documents should apply to the NATO Archives in Brussels.