British Rail Class 31 diesel locomotives

Design and characteristics

Class 31s are diesel-electric locomotives with a Bo‑Bo wheel arrangement, reflecting their role as versatile mixed-traffic engines. As a Type 2 in British Rail terminology, they offered moderate power and were designed for reliability and ease of maintenance. Over their working lives some members of the class received modifications to improve braking, train heating and multiple-working capability.

History and development

The locomotives were ordered during the post‑war modernization program that replaced steam traction on many secondary routes. Built between 1957 and 1962, they entered service with British Rail in a variety of liveries and allocations. Early operational experience led to progressive changes and the class was later renumbered and reclassified under the TOPS system; original references as Class 30 appear in early records.

Roles, examples and later life

Throughout their career Class 31s worked passenger expresses, local stopping services, parcels and light freight trains. As newer, more powerful diesels and multiple units arrived, many Class 31s were cascaded to secondary duties or transferred to departmental use. Several examples have survived into preservation and operate on heritage lines, where they represent mid‑20th century diesel development.

Notable facts and distinctions

• Often described as a dependable mixed-traffic locomotive, suitable for a wide range of duties.
• Subject to numerous sub‑class modifications during their service life, reflecting operational needs.
• Remains well represented on heritage railways and enthusiast circuits, with technical and historical material available through specialist sources such as class histories and preservation groups.