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
Class 122, no. 55006, at Bewdley on the Severn Valley Railway 2004, whilst taking part in the Railcar 50 event. This unit is painted in the second version of BR Green livery, and is preserved on the Ecclesbourne Valley Railway.
Derby Lightweight no. 79900 operating on the line on which it was originally tested when new some 55 years earlier, fully restored to passenger carrying standard from being former test car ”Iris”. It is now a preserved example of a Derby Lightweight single car unit.