Coupling code: Blue Square (later Red Triangle)
Underframe: 64ft 6in
Engines: Rolls Royce 238hp
Thirty of these sets were built, each formed of 2xDMBS, TS and TSL. They were high density sets with no gangway connections, with seats for 352 2nd class passengers, later reduced to 348. Rarely venturing from the intensively worked St. Pancras to Bedford line, this earned them the name Bed-Pan units.
Built with a blue square control system problems with driver errors when coupled to gearbox units meant the vehicles were reclassified as red triangle units.
They lasted in passenger service on the line until electrification in '83 when the power cars were withdrawn, although a good few went into parcels use. A lot of trailers were transferred to Tysley and lasted another ten years.