Class 316 and 457

To help develop the Class 465 "Networker" multiple-unit BR took 4 coaches from the Class 210 DEMU and used them as a test bed, firstly as the Class 457 for DC third rail and later as the Class 316 for AC overhead [1]. The former Class 210s were converted at RTC Derby and then ran for a while on Southern Region. The 457s were fitted with three-phase traction motors which allowed for significant energy savings over earlier types of motor [2].

Information
Number built: 4 (1 4-car set)
Built: 1989-90 (Class 210s originally built 1981)
Builder: BREL Derby
Engine: Brush three-phase traction motors (750v DC third rail (457) 25kV AC OHLE (316))
Power: 1, 140 hp (850 kW) 
Formation: (457) Driving Motor Standard Open (DMSO)+Trailer Standard Open (TSO)+TSO+DMSO
(316) DMSO+Pantograph Trailer Standard Open (PTSO)+TSO+DMSO

Later they returned to Derby and were converted to AC traction by inserting a PTSO from a Class 313 and worked AC electrified lines North of the Thames. Of the 4 cars used 2 have been converted to and form part of Class 455/9 EMUs, and 67300 has been preserved.
67300 at the Electric Railway Museum

[1] Colin J Marsden, DMU and EMU Recognition Guide (Ian Allan, 2013) p. 355
[2] Alec Swain, Overhead Line Multiple Units (Ian Allan, 1990) p. 80