The class 50's were built by English Electric between 1967 & 1968 and a total of 50 were introduced to power west coast services north of Crewe prior to electrification of the route and once this was completed they were transferred to the western region. The class was dogged by reliability problems and were progressively refurbished during the 1980's with redundant equipment removed. The 50's were largely based at Old Oak Common, Bath Road and Laira and finished regular main line service by 1992.