a six-hour schedule for the "Royal Scot" London Euston-Glasgow Central and v.v. service). Once the electric service was introduced as far as Preston in 1973, this double-heading by Class 50s transferred there, although poor availability often resulted in single-heading with consequent delays. The ability to operate using multiple working had been part of the locomotive's initial design brief, but only two of the class had the facility from new, but with the introduction of the regular double headed duties, this facility was fitted to the whole class. By 1974 the northern WCML was electrified, and the Class 50 fleet was displaced by new Class 87 electrics. The fleet was transferred to the Western Region between 1972 and 1976, working mainline passenger services from London Paddington along the Great Western Main Line (GWML) to destinations such as , Bristol Temple Meads, and . It was not unusual for locomotives to work services on other routes, such as the Birmingham New Street to Bristol Temple Meads corridor. The introduction of the Class 50s on these routes enabled the last remaining, non-standard, diesel hydraulic "Westerns" to be withdrawn. In the late-1970s, following a period where the policy of locomotive naming had been abandoned, BR was persuaded to name the class 50s after Royal Navy ships with notable records in World War I and II. As a result, the first locomotive naming occurred in January 1978, when 50035 was named Ark Royal by the captain and crew of then current aircraft carrier HMS Ark Royal. The rest of the fleet was named during the course of the next few years. 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. Refurbishment To deal with increasing reliability problems, the Class 50 fleet was refurbished at Doncaster Works between 1979 and 1984. Doncaster had taken responsibility for the fleet after BR completed the purchase of the