This section also covers the post-privatisation period, as the broad numbering and classification arrangements have not altered since the break-up of BR.
Locomotives and multiple units (the majority being self-propelled) have frequently had similar arrangements for classification and numbering, so are considered together here.
In 1948, BR inherited a variety of locomotives and multiple units from the Big Four railway companies and some smaller concerns.
Details of the numbering and classification systems used by the Big Four companies are covered in the following pages: In the main, new locomotives and multiple units built by BR to pre-nationalisation designs were numbered and classified according to the principles applied by the relevant Big Four company.
To classify electric stock, a two-letter prefix was used to indicate what type it was, followed by a number issued sequentially from 1.
The first method was also adapted from the old LNER system, and applied only to diesel shunters operating on those regions.
It comprised a prefix, indicating the transmission type and wheel arrangement, followed by a number allocated sequentially from 1.
The prefixes used were: The second classification system was developed in 1955 and applied to all types then in existence on British Rail.
Locomotives were given a two-letter code, with the second letter indicating detail differences within the main type.
In the early period of British Railways, steam locomotion had continued to be of prime importance.
The numbering system matched up the new 'Type' classification that had been adopted for diesel traction, and which was based on the power of the locomotive.
When the last mainline steam locomotive was withdrawn in August 1968 (leaving only three on the self-contained narrow gauge Vale of Rheidol Railway), the 'D' prefix was dropped.
This was usually where sub-classes had already been or were in the process of being created (for example classes 45 and 47, in which some members were being fitted with electric train heating equipment, and 86, subject to various modifications, mainly to the suspension).
Please Note: This section explains the successful application of TOPS to multiple unit stock, the arrangement that persists today.
Class 01 was subsequently reused to register any ex-industrial/Ministry of Defence shunters used on the national network regardless of horsepower.
When Southern Region unit numbers were changed to fit with the TOPS classification system, former 4x0 classes were all reclassified to 4x2.
In September 2011, the UK Rail Safety and Standards Board issued Railway Group Standard GM/RT2453,[4] which made some alterations to the TOPS classes allocated to various types of locomotive and multiple unit - primarily extending the number ranges for certain types of locomotives and multiple units where the previous allocation ranges were becoming exhausted.