The Pacer series was the outcome of an idea to try using bus parts to create a diesel multiple unit. The first prototype, known as LEV 1, was made by British Rail Research Division and Leyland Motors working together. It used a bus body that was mounted on a modified freight train underframe (HSFV1). In 1980 they also built a two-car prototype class 140 at British Rail Engineering Limited (BREL)'s Derby Litchurch Lane Works.