The British Rail Class 122 diesel mechanical multiple units were built by Gloucester RC&W in 1958. Twenty single-car, double-ended driving motor vehicles, nicknamed "Bubble Cars", were built, numbered 55000–55019. These were supplemented by nine single-ended trailer vehicles, numbered 56291–56299

The Class 122s were built mainly for use on the London Midland Region of British Railways, although some were also used in Scotland. They were used on a variety of lightly used lines, many of which were closed during the Beeching Axe in the 1960s including the ex-LSWR lines in West Devon and North Cornwall. Routes served included the Stourbridge Town and St Albans Abbey branch lines, as well as local services between Dundee and Arbroath. (The similar Pressed Steel Company built Class 121 single units were also used on the Western Region).

During the 1990s, refurbished Class 122 units were used on the Cornish branches between Liskeard and Looe and St Erth and St Ives.

8 cars have been preserved.