British Rail Class 31

The British Rail Class 31, also known as the Brush Type 2, is a class of diesel-electric locomotive built for British Railways during the first major phase of dieselisation. Constructed by Brush Traction at Loughborough between 1957 and 1962, the class became one of the best-known medium-power British diesel types and earned a reputation as a flexible, widely deployed “general purpose” locomotive for secondary passenger trains, parcels, trip freight, engineers’ workings and a range of other duties.

A total of 263 locomotives was built. They were initially numbered D5500–D5699 and D5800–D5862, later becoming 31001–31970 under the TOPS numbering system. The earliest batch was briefly identified as Class 30 under TOPS because of its original engine type, with the rebuilt locomotives later standardised as Class 31 after re-engining.

Class 31s worked across most regions of British Rail over their long careers. Although the type was introduced primarily for the Eastern Region, it later became common on the North Eastern, London Midland and Western regions, and also saw regular use in Scotland and on cross-country or transferred duties as fleet needs changed. In preservation, the class has survived in large numbers and remains one of the most familiar diesel classes on heritage railways.

Background and procurement

British Rail’s Modernisation Plan created demand for new diesel locomotive types to replace steam traction on a broad range of duties. In the mid-1950s, BR adopted a “pilot scheme” approach, ordering multiple designs to evaluate performance and maintenance requirements under real operating conditions. The Brush Type 2 formed part of that wider push, aimed at creating a medium-power locomotive capable of handling mixed traffic and secondary passenger duties where a larger Type 4 would not be required.

Brush’s design drew on export experience and contemporary diesel-electric practice. The locomotive used a diesel engine driving a generator, with traction motors providing power to the axles. The chosen wheel arrangement was A1A-A1A, meaning each bogie had three axles but only the outer axles were powered. This reduced axle load and track forces compared with a fully powered Co-Co arrangement, and was intended to give adequate adhesion for the locomotive’s power rating while allowing broader route availability.

Construction and basic design

The Class 31 was built with a full-width body and cabs at each end, with central engine room and electrical compartments. It was a diesel-electric design and, as built, carried a Mirrlees JVS12T engine in the early period. The class used Brush electrical equipment and four traction motors (one on each powered axle).

The A1A-A1A arrangement made the class distinctive among BR diesels. In service, it contributed to the locomotive’s reputation as a capable but not exceptional hauler in difficult conditions, particularly on heavy freight starts where fully powered bogies could have an advantage. However, the layout also helped the class work over a wide range of routes and made it suitable for passenger work where high continuous tractive effort was less critical than reliable running and reasonable acceleration.

Early locomotives had external differences from later production. The first 20 locomotives, D5500–D5519, lacked the later headcode box arrangement above the cab windows. Enthusiasts later described these as “skinheads” because of the cleaner cab-front appearance. Over time, other equipment and body details also varied as the class was modified, rebuilt and refurbished.

Engines, re-engining and the change from Class 30 to Class 31

The defining technical story of the class is the replacement of the original Mirrlees engines. The early Mirrlees installations proved unsatisfactory in service, and British Rail pursued a programme to fit the type with English Electric 12SVT engines instead.

A successful trial installation led to a systematic re-engining programme across the fleet. Between the mid-1960s and late 1960s, the locomotives were progressively converted. This uplifted both reliability and the effective usefulness of the class, although power output was limited by what the existing electrical system could accept.

This programme also drove the confusing identity change in TOPS-era classification. The Mirrlees-engined examples were initially recorded under Class 30, while re-engined locomotives were treated as Class 31. As rebuilding progressed, the fleet consolidated into the Class 31 identity, and “Class 30” became a brief historical footnote rather than a continuing subtype.

Subclasses and variations

In practice, several subclasses and operational variants existed, reflecting equipment and role changes.

Class 31/0

The first batch is often grouped as 31/0, including locomotives with early control equipment and the most distinctive external appearance. Many of these were withdrawn earlier than the main fleet because they were more non-standard.

Class 31/1

The main production standard became 31/1, representing the bulk of the fleet in general-purpose condition. These locomotives were widely used on passenger, parcels and freight work.

Class 31/4 and ETH capability

A later and operationally important variation was the 31/4, fitted with Electric Train Heating (ETH) equipment. This allowed the locomotives to heat electric-heated coaching stock, expanding passenger usefulness in an era when steam heating was disappearing. ETH-fitted locomotives became more valuable for passenger duties, charters and certain departmental roles.

Departmental and other modifications

Over time, some locomotives were modified for departmental and specialist work, including route learning, test trains, engineers’ duties and conversions to other TOPS categories. A small number were classified under other series for departmental reasons, reflecting how BR managed specialist fleets.

Allocation and operating regions

The class was initially closely associated with the Eastern Region, with early allocations to depots such as Stratford and March. In the early years, they were used on a variety of passenger and parcels duties in East Anglia and North East London, and they also worked freights where their power and availability suited.

Over time, the Class 31’s operational geography expanded significantly:

• Eastern Region: secondary passenger trains, parcels, and trip freights, plus empty coaching stock moves in the London area and East Anglia.
• North Eastern Region: mixed-traffic duties and secondary passenger work, including services on routes where steam was being eliminated.
• London Midland Region: passenger and freight duties, including services in the Midlands and north-west where the class could substitute for other types.
• Western Region: later use included empty coaching stock work and secondary passenger duties, particularly as locomotives moved between regions in response to fleet needs.

This wide spread of use is one reason the class became so familiar. Many diesel classes had strong “home” regions, but the Class 31 increasingly became a locomotive you could see almost anywhere on the network, especially on less glamorous trains.

Passenger duties

The Class 31 was never a flagship express locomotive. Its passenger role was mainly on:

• secondary and stopping services
• cross-country diagrams where moderate power was acceptable
• empty coaching stock moves
• holiday extras and seasonal trains
• later, charter and railtour work

In the pre-ETH period, the class used steam heating for coaching stock, and in later years ETH-fitted 31/4s extended usefulness on passenger operations. As the passenger coaching stock fleet modernised, ETH became an important discriminator between locomotives that could still work passenger diagrams and those largely confined to freight or departmental roles.

Class 31s were also used with multiple working systems (notably the Blue Star system on many locomotives), allowing double-heading and occasional multi-loco freight or passenger arrangements. While not as common as on some other classes, this capability supported flexible use in busy areas and during shortages.

Freight and parcels work

Freight use formed a substantial part of the class’s career, though the locomotive’s power meant it was generally used on lighter or medium freight duties rather than the heaviest block trains. Common freight and parcels roles included:

• trip freights and local distribution work
• parcels and newspaper trains
• departmental trains and engineers’ workings
• wagonload services and pick-up goods
• occasional heavier freights where multiple locomotives could be used, or where gradients and timings allowed

In the late BR period, as wagonload freight declined and freight sectors changed, Class 31s often remained useful because they were paid off, well understood, and capable of covering a wide variety of “odd job” duties that did not justify newer or larger locomotives.

The class in the sectorisation and privatisation eras

During the sectorisation era, Class 31s appeared in a wide range of liveries aligned with passenger and freight sectors. The class became strongly associated with the everyday railway rather than prestige sectors, although individual locomotives and regions could produce distinctive appearances and roles.

In the privatisation era, the class’s main line role shrank but did not disappear immediately. Individual locomotives moved through several commercial and leasing arrangements, appearing with operators and owners involved in infrastructure, charter, and short-notice cover. A small number remained active for specialist duties long after the class had ceased to be a mainstream BR workhorse.

Withdrawals began relatively early for the most non-standard locomotives, but the class as a whole had a long tail of service. The final main line withdrawals took place in the 2010s, depending on operator, overhaul condition, and demand for heritage and special workings.

Nicknames and cultural profile

Class 31s accumulated a range of informal nicknames over their careers. Some were linked to sound, appearance, or early control arrangements. While nicknames are not central to the technical history, they reflect how familiar the class became to railway staff and enthusiasts.

The class’s cultural profile also benefited from its ubiquity. Unlike rarer locomotives that became famous for novelty, the Class 31 became well known because it was routinely seen on ordinary trains in many regions for decades.

Preservation and surviving examples

Preservation of the Class 31 has been notably successful. Dozens of locomotives survive, and the class remains common on heritage railways. Preservation has taken several forms:

• locomotives maintained for heritage line use, including passenger and demonstration services
• locomotives restored for main line charter work (where equipment and certification allow)
• static or long-term restoration projects, often used for spares support and future overhaul planning

A key preserved example is D5500 (later 31018), the first of the class, which survives in the national collection. This locomotive is significant as a representative early Brush Type 2 and a tangible link to the first phase of BR pilot scheme dieselisation.

A1A Locomotives Ltd and organised preservation

One of the best-known dedicated Class 31 preservation organisations is A1A Locomotives Ltd, which describes itself as a Class 31 preservation body and operates and maintains multiple locomotives. The group has a long-running association with the type and has preserved locomotives in both unrefurbished and refurbished forms, reflecting different eras of Class 31 service.

Groups like A1A Locomotives illustrate an important reality of preserving mid-century diesel traction. Sustaining a large locomotive class requires secure sites, engineering capability, and long-term parts planning. The Class 31 has benefited from being built in significant numbers, which increases parts availability and donor potential, and from continued enthusiast interest that supports restoration work.

Heritage railway examples

Class 31s are widely spread across heritage lines. Many railways value them because they are powerful enough for passenger service, relatively compact compared with some larger Type 4 locomotives, and practical for routine operation. The type’s long BR career also means that it suits a wide range of heritage themes, from early dieselisation to late BR regional and sectorisation periods.

Historical significance and legacy

The British Rail Class 31 is historically important for several reasons.

1. A major early diesel class: It was built during the decisive early phase of BR dieselisation and formed part of the pilot scheme era that shaped later procurement decisions.

2. A long-lived mixed-traffic workhorse: Few diesel classes matched the Class 31’s breadth of routine duties across passenger, parcels, freight and departmental work over such a long period.

3. A clear example of BR rebuilding policy: The transition from Mirrlees engines and the “Class 30” identity to the re-engined Class 31 fleet shows how BR adapted and standardised early diesel types to improve reliability and reduce non-standard maintenance burdens.

4. Strong preservation outcome: With a large number preserved, the Class 31 is one of the best-represented BR diesel classes in heritage operation, ensuring the type remains visible and operational for modern audiences.

In summary, the Class 31 was not a locomotive built for glamour. It was built to do everyday work across a changing railway. That is also why it became one of the most familiar diesels of the British Rail era, and why it continues to be a mainstay of diesel operation in preservation.