The records in RAIL are those of all private railway companies and private canal companies taken into public ownership by the Transport Act of 1947, together with records which relate to the railway network, and those of associated bodies.

They are as follows:

• the records of the Great Western Railway Company (GWR), the London Midland and Scottish Railway Company (LMS), the London and North Eastern Railway Company (LNER), and the Southern Railway Company (SR), together with their associated undertakings;
• the records of private canal companies;
• the records of the London Passenger Transport Board, 1933-1947;
• and other railway records, from both private and public sources, relating mainly to the pre-nationalisation period.

These records relate to all administrative and operational aspects of private railway and private canal companies, to the railway network, and to their associated functions.