156406 near Attenborough in July 2009. © Duncan Harris
Built by Metro-Cammell in a batch of 114, the Class 156s were commissioned by British Rail to replace ageing first-generation DMUs and loco-hauled passenger services. The class were intended for use on longer journeys with fewer stops, so were fitted with single-leaf doors at the ends of each coach. The 156s have seen heavy use over the years on lines across Scotland, Northern England, the Midlands and East Anglia. The whole fleet are still in service today, as of 2021, and look to be in use for the forseeable future.
(Information provided via Wikipedia)