From 1782 to June 1920 most Treasury papers were registered in annual numerical series and are to be found mainly in the single series, T 1, although there are a few supplementary papers in T 89.
Following the reorganisation of 8 June 1920 a separate registered file series was created for the divisions of each of the three departments with an additional general file series for subjects which were not adjustable to any single department. In addition to the F (for Finance), S (for Supply), E (for Establishment) and G (for general) there was a fifth, P series for the Superannuation Division in the Establishment Department. These five series will be found in T 160, T 161, T 162, T 163 and T 164 respectively.
This central registry system was based on the 'Treasury Theme System', whereby one file, registered under its own number, was created for the papers on each single subject. Files were given numbers consecutively in each of the five series as they were opened, the numbers having no subject significance of their own. When a file on a subject subsidiary to an existing main subject needed to be opened, it was given the number of the main subject file with a subnumber prefixed by a zero, eg S25/01. Where a hierarchy of subsidiary subjects needed to be used, a succession of zero prefixed subnumbers could be given. If a file became too thick, it was divided into parts with subnumbers not preceded by a zero, eg S3732/1. The central registry maintained a subject index to each series, based on main headings, subheadings and divisions of subheadings, further explanation of which will be found in a Key to Treasury Files in T 160, which is available in the reading rooms at The National Archives, Kew.
In 1948, following two reports of the Organisation and Method Division in 1946, the central registry was replaced by decentralised sections working to a division or set of divisions. Files that were still current in each of the central registry series were then re-registered in the new divisional files series, each of which was given a prefix based on the divisional title. The Social Services Division, for example, was given the prefix SS and each of these series is found in a separate record in the groups of Finance divisions, Economic Planning divisions and Establishment and Supply divisions, in this case T 227 in the latter.
The policy files in these series have a reference code made up of the divisional prefix followed by primary and secondary numbers denoting subjects followed by a sequence number, eg SS22/476/01. If the file was split a final letter would be added. The subject headings represented by numbers came from a master list known as 'The Bible' controlled by the Chief Registrar. Case papers, few of which survive, used the same prefix but represented subjects by a letter followed by a sequence number, eg SSB/2.
In April 1960 the filing system was again reorganised in order to implement the Grigg Committee recommendations on Public Records. Generally, each file series was closed and a new series started using the same divisional prefix but with the number 2 added, eg 2SS. These series ended in October 1975.