Birmingham Railway Carriage & Wagon Company built Sulzer engined type 2 diesel locos, a slightly more powerful evolution of class 26. 69 were built between 1961 and 1962. Between 1971 and 1973 24 were dual braked and renumbered into class 27/1 for use with MKII push-pull formations working Glasgow to Edinburgh services. Between 1974 and 1975 12 class 27/1 were fitted with electric train heating equipment and renumbered into class 27/2 and used on the push-pull trains with a class 27/1 at the opposite end. The introduction of class 47/7 locos in push pull mode with MKIII rakes and a MKII DBSO on the Glasgow to Edinburgh services saw the remaining class 27/1 and 27/2 locos renumbered into the class 27/0.