|Number built:||40 (10 4-car sets)|
|Engine:||2 BUT (Leyland Albion) 6-cyl per power car|
|Power:||920 hp (686 kW)|
|Formation:||Driving Motor Brake Standard Lavatory (DMBSL)+
Trailer Composite Corridor (TCK)+Trailer Standard Lavatory or
Trailer Buffet Standard (TSL/TSLRB)+
Driving Motor Standard Corridor (DMSK)
The Class 123 was also fitted with Pullman style gangways to the cab ends so everyone on a train could access the buffet car. They were used on South Coast-Wales services though were based on Western Region as Southern Region did not want to have anything to do with diesel-mechanical units! They were later used on outer-suburban services out of London Paddington .
They were surplus to requirements by the late 1970s but had a short reprieve in the North East of England before finally being withdrawn in 1984.
|Class 123 at Swindon (KD Collection)|
 Brian Haresnape, Diesel-Multiple Units: The First Generation (Ian Allan, 1985) p. 71
 David Lawrence, British Rail Designed 1948-97 (Ian Allan, 2016) p. 135
 Colin J Marsden, DMU and EMU Recognition Guide (Ian Allan, 2013) p. 83