British Rail locomotive and multiple unit numbering and classification

A number of different numbering and classification schemes were used for locomotives and multiple units operated by British Railways (BR), and this page explains the principal systems. 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. There are also links to other pages that deal in greater depth with the particulars of individual types.

Constituent companies
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:
 * Great Western Railway: GWR locomotive numbering and classification
 * Southern Railway: SR locomotive numbering and classification and SR multiple unit numbering and classification
 * London, Midland and Scottish Railway: LMS locomotive numbering and classification
 * London and North Eastern Railway: LNER locomotive numbering and classification

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.

1948 numbering and classification
Immediately after nationalisation, BR had to decide how to number and classify the stock it had inherited from the 'Big Four' companies, and how newly-built stock would be included. In the main, it decided to simply adapt what was already there.

Locomotives
The classification systems of the 'Big Four' were left unchanged for the inherited locomotives. However, BR decided to adopt the LMS power classification system as its preferred model and all inherited locomotives received a classification in this series as well as their traditional classification.

In order to remove the duplications of locomotive numbers, all locomotives were placed into a new number series as follows:

Note: *Isle of Wight locomotives retained their existing numbers in a separate series commencing at W1, and locomotives transferred to the island by BR were renumbered into that series - and vice versa for those returned to the mainland.

This approach meant that the numbering arrangements adopted by the pre-Nationalisation companies were retained in the new system, and new locomotives built to the designs of the old companies were numbered appropriately in their series. Locomotives inherited from smaller concerns were numbered in the most appropriate regional list, e.g. ex-East Kent Railway stock utilised blank numbers in the 3xxxx ex-SR series.

The new series for diesel, petrol, gas and electric locomotives were arranged as follows:

Note: * Number 13000 was initially allocated to a 250 hp (186 kW) ex-LMS shunter, but this locomotive was withdrawn before being renumbered.

Modern traction
Numbering of electric multiple units was undertaken on a regional basis, with each region having its own series commencing from 001. Most diesel multiple units were not allocated unit numbers, though in later years numbers were allocated on a regional basis in the Scottish and Western regions, and by individual depots elsewhere. For more details on these series, see British Rail Regional Multiple Unit Numbering.

To classify electric stock, a two-letter prefix was used to indicate what type it was, followed by a number issued sequentially from 1. This was a system adapted from that used by the LNER for its electric stock (e.g. EM1, see here). The additional prefixes used were:
 * AL: AC electric locomotive
 * AM: AC electric multiple unit

The Eastern and North Eastern Regions used a series of different classifications for diesel locomotives. 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:
 * DEJ: Diesel-electric, 0-6-0 wheel arrangement
 * DJ: Diesel-mechanical or hydraulic, 0-6-0 wheel arrangement
 * DY: Diesel-mechanical or hydraulic, 0-4-0 wheel arrangement

The second classification system was developed in 1955 and applied to all types then in existence on British Rail. It was based on the format Dx/y, where x was the power of the locomotive in hundreds of horsepower and y was a number allocated sequentially to specific types (e.g. D1/1 would be a shunter with a 100 to 199 hp (75 to 148 kW) rating, D33/1 would be a Type 5 locomotive). The series was extensively re-arranged in 1962 in a somewhat confusing way, but following the same basic principles.

The Southern Region followed existing numbering (for its multiple units) and classification systems (for both multiple units and locomotives) inherited from the SR. The EMU classification system (e.g. 4SUB, see here) system was also extended to include their diesel-electric multiple units, but with a single letter. Locomotives were given a two-letter code, with the second letter indicating detail differences within the main type. For instance, what were to become Class 33 locomotives from 1973, were Class KA or KB depending on whether they were the standard design or that fitted for push-pull working with 4TC units.

1957 numbering and classification
In the early period of British Railways, steam locomotion had continued to be of prime importance. Apart from a growing selection of diesel shunters, there had been almost no development of mainline diesel or electric traction beyond the few locomotives ordered by the 'Big Four' companies.

The 1955 Modernisation Plan heralded big changes in this situation, and from 1957 a new numbering system was used for diesel and electric locomotives ordered by British Railways, including those shunters ordered before 1957, which were renumbered into the new system. All steam and gas-turbine locomotives, and diesel and electric locomotives built to pre-nationalisation orders retained their existing numbers under the 1948 arrangements, though some had a 'D' or 'E' prefix added to their number in error.

Diesel locomotives
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. The broad categories were as follows:

Of the shunters that were renumbered, the only transparent renumbering was for those that had been numbered in the 13xxx series, for which the '1' was simply replaced with a 'D'. All the others were completely renumbered to separate out the different classes.

As always, there were some oddities. The 650 hp diesel hydraulic locomotives later Class 14 were numbered from D9500 upwards. When the Type 2 series got too crowded later on, new Sulzer Type 2 locomotives (later British Rail Class 25) were numbered from D7500 upwards. Some experimental locomotives carried D0xxx numbers.

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.

Electric locomotives
The numbering system was divided into two series, one for AC locomotives and one for DC locomotives. DC locomotives were numbered from E5000 upwards, and DC electro-diesel locomotives, with a diesel generator for working off electrified lines, were numbered from E6000 upwards.

For AC locomotives, the first number was to be an indication of power. For example, if the power was in the range 2000 to 2999 hp, it would be numbered between E2000-E2999, and so on. In fact, apart from E2001 (the prototype AC locomotive, converted from a gas turbine locomotive, later Class 80), all AC locomotives were numbered from E3001 upwards. When new 5000 hp locomotives were under construction (later Class 87), these were allocated numbers from E3201 upwards, though they never carried these numbers as the 1973 arrangements were already in place by the time the first one was built.

1973 numbering and classification - TOPS
At the end of the 1960s, British Railways adopted the Total Operations Processing System (TOPS), a computerised system developed by the Southern Pacific Railroad in the United States. All types of locomotive and multiple unit received a TOPS classification, according to this broad division:

From 1973, British Railways started to apply new numbers to locomotives and multiple units based on the TOPS classification system. The format of these numbers is xxxyyy, where xxx is the class number and yyy the unique identifier for that locomotive or unit. All locomotive classes have unique identifiers that commence at xx001, except classes 43 (originally treated as multiple unit carriages), 97 and 98 (departmental and steam locomotives). Multiple unit classes are treated differently, because an attempt has been made to give units working within the same region or sector unique identifiers (for more information see British Rail Regional Multiple Unit Numbering). In recent years, unit numbers have also been tied in with the numbers of the carriages within a unit (e.g. 150201 is formed of carriages 52201 and 57201). As a result, very few multiple unit classes commence from xxx001.

Where there are variations within a class, subclasses are used in the format xxx/y. Usually, the subclass is connected to the first digit of the unique identfier, so that the first locomotive in subclass 47/3 was 47301. However, some caution is required on this point for the following reasons:
 * Where there are more than 100 examples in a subclass the identifier becomes obscured, e.g. 31201 is in subclass 31/1, which runs from 31101 to 31327.
 * Some classes renumbered from the 1957 arrangements simply had consecutive numbers from xx001, which ignored the subclasses identified, e.g. 25033 was in subclass 25/1.
 * Where numbers within a class became congested, it wasn't always possible to make the connection, e.g. locomotives in subclass 47/2 were numbered downwards from 47399. In other cases it wasn't possible to start from xxxy01, e.g. subclass 08/9 started from 08991 because subclass 08/0 ran from 08001 to 08958.
 * Because of the different arrangements for numbering multiple units (see above), subclasses may have no link to the unique identifier at all; this is especially true on the Southern Region. Sometimes, where there is a principal run of units and a small variant subclass, the majority will be subclass xxx/0 whatever their identifier, but the variant's subclass does reflect the identifier, e.g. Subclass 302/0 for the standard passenger units (302201-312) and 302/9 for the postal units (302990-302993).

So far as renumbering from the 1957 arrangements was concerned, most locomotives retained the last two digits of their number, though some classes were renumbered without reference to their previous numbers. This was usually where sub-classes had already been or were in the process of being created (for example Classes 45 and 47), but some classes were renumbered randomly for no apparent reason (for example Class 86). The other exception was the first locomotive of each class, which had usually carried Dxx00 numbers under the 1957 arrangements, since TOPS could not handle numbers ending in '000'. These were often renumbered to the end of the class (e.g. D400 became 50050), or took the number of another class member that had already been withdrawn (e.g. D5000 became 24005).

The situation was different for multiple units. Where unit numbers were carried, they were usually three-digit already. TOPS simply prefixed these existing unit numbers with the newly-allocated TOPS class number. The process was more complicated on the Southern Region, which used four-digit unit numbers and where a more general unit renumbering was required so that the first number of the unit coincided with the last digit of the class number. Many diesel multiple units were not kept in regular formations, so did not have existing unit numbers, and this situation was not changed under TOPS (except following refurbishment).

The TOPS system has been perpetuated by the privatised railway, though the allocation of classes and numbers appears to have become more random and less governed by the rules followed by British Railways (but even they made exceptions). See British Carriage and Wagon Numbering and Classification for an explanation of how TOPS applied also to carriages and wagons.

Please Note: This section explains the successful application of TOPS to multiple unit stock, the arrangement that persists today. However, there was an earlier attempt to apply TOPS that differed from the arrangement set out below. More details about the first arrangement may be found here.

Locomotives
The series of locomotive classes were allocated according to the following pattern:

The following table shows in more detail how the classification of diesel locomotives was overlaid on the 1957 classification by Type:

AC electric locomotive classes AL1 to AL6 became 81-86 in order.

Multiple units
The multiple unit series were divided up as follows:

AC electric multiple units AM1-AM11 became 301-311 in order (in fact the AM1 units had already been withdrawn, so Class 301 was never actually used). The 1xx and 2xx series were originally arranged so that driving motors, driving trailers and trailer cars all had their own individual class numbers (presumably because these units were more prone to being reformed), but this was subsequently revised so that each type of unit had a single class number, as allocated to the driving motor car.

Whereas within most ranges class numbers were allocated sequentially as new types were constructed, the Southern Region adopted a more complicated system for their electric multiple units, with the second and third digits indicating in more detail the type of unit. Second digits were allocated as follows:

Third digits were allocated as follows:

Of course, many exceptions arose over time. One major change was to change the classification of unpowered trailer units from 49x numbers to 4x8 numbers (which involved reclassifying Class 491 to Class 438). When Southern Region unit numbers were changed to fit with the TOPS classification system, former 4x0 classes were all reclassified to 4x2. This was necessary because Southern Region units only displayed the last four digits of their six-digit TOPS number, and it was decided that no painted unit number should commence with a '0'. It is worth noting that despite only showing the last four digits, the actual number of the unit was still the six-digit TOPS number. This often causes confusion both to enthusiasts and those outside the field alike.