From 1977, British Rail introduced InterCity 125s onto the Great Western Main Line which began the displacement of the Class 50 fleet onto other routes, such as services to Birmingham New Street from London Paddington and Bristol Temple Meads. The class also found work on the West of England Main Line from London Waterloo to , Exeter and . However, due in part to the over-complexity of the design, the class was plagued with reliability problems which resulted in frequent service failures and cancellations. As a result, the decision was taken in the late 1970s to refurbish the entire fleet.