Class 321s were originally built for the Bedford services. However, in 1990, they started being used on Great Eastern Main Line services to Southend Victoria, Braintree and Clacton, to replace the class 302 and 305 EMUs, many of which were approaching 50 years old. Some 321s (many of the 3214s) were sent to work inter-regional services for Silverlink, and then briefly for London Midland, primarily on Euston to Northampton/Milton Keynes/Tring services.