BR ordered ten new Co-Cos from Derby Works as part of its appraisal of comparative locomotive designs (dubbed the ‘Pilot Scheme’). They were inspired by the LMS’ and Southern’s pioneer diesel designs and were outwardly similar to English Electric’s Type 4 (subsequently Class 40). Although fitted with a Sulzer 12LDA28 diesel engine capable of 2,300hp, the new BR Type 4s were heavy. Their 133 ton weight required a 1Co-Co1 wheel arrangement.

The first, D1, emerged from Derby in 1959 and was named Scafell Pike. The remaining nine locomotives were also named after English and Welsh peaks and the class soon gained the nickname ‘Peak’, which was also applied to the subsequent Class 45s and Class 46s.

Although a mixed traffic design, they were initially used on West Coast Main Line passenger services before being transferred en masse to the Midland Main Line. The subsequent arrival of the Sulver Type 4s (later Class 45) meant that the BR Type 4s (which would become Class 44 on TOPS) were allocated predominantly to freight work radiating out from Toton. Consequently, they could be seen as far afield as York or Severn Tunnel Junction.