Portsmouth Harbour and later on the Heart of Wessex line. Over time they were displaced from most passenger work by new build DMUs such as the Sprinter units, though they still found work in the summer and on secondary services from time to time through the 1990s as traffic demand required. This saw use both on the North Wales Coast and, most remarkably, Cardiff–Rhymney local services through to 2006. In Scotland after being displaced from the West Highland and far north routes, 37/4s were used on two diagrams on the Inverness–Edinburgh route for several years as well as being used to Kyle of Lochalsh in the summer and on Inverness–Aberdeen services. The final daily work in Scotland was the Fort William Caledonian Sleeper, this ending in June 2006. Their freight work similarly reduced, being displaced by higher powered locomotives such as the Class 56 and Class 58 locomotives on coal trains, though they continued on other cargos such as oil tankers for longer. After privatisation In the 1980s, many locomotives were refurbished, which has contributed to the Class 37 fleet becoming one of the longest surviving classes on British railways. However, the introduction of new Class 66 locomotives has meant many 37s have been withdrawn or scrapped. English Welsh & Scottish and Direct Rail Services operated small fleets, with several other examples also operated by spot-hire companies. However, second-hand Class 37s have also proved popular in the export market, with some examples operating in Spain and France, serving the construction of those countries' high-speed railway networks. As of 2022, numerous examples of the class are still in mainline service, despite all of them being more than fifty-seven years old. Colas Rail Colas Rail owns ex-preservation 37057, 37099, 37116, 37175, 37219, 37254, 37421, all currently operational. Additionally, Colas purchased 37146, 37188 and 37207 with the intention of returning them to main line duty but, as of March 2020, 37146 is unlikely to receive its intended overhaul and is expected to be sold or used as a parts donor. 37188 was broken up at UK Rail Leasing's Leicester depot, in 2019. Between July 2019 and March 2020, three Colas Rail Class 37s (Nos. 37025, 418, 421) operated peak time loco-hauled services on the Rhymney line with eight Mark 2 carriages, the first passenger loco-hauled services on the route since 2005, due to a lack of rolling stock caused by the two-year delay