The British Rail Class 203, initially classified 6B, was a type of diesel-electric train. Seven units, numbered 1031-1037, were constructed in 1958 for use on the Southern Region. They were similar to the earlier Class 202 units, differing only in the substitution of a trailer buffet car for one of the three trailer second opens.

Two vehicles survive: DB975025 Caroline and S60750. S60750, the buffet removed car from unit 1031 in 1963, had been used for tilt tests in the 1980s for the Advanced Passenger Train. This vehicle was fitted with a centre executive section, a urinal, and a classroom at one end which also had windows fitted for use when the vehicle was propelled at the Old Dalby test track, and was later used for airflow tests before being rescued first by Hastings Diesels Ltd at St. Leonards Depot and subsequently by the Hastings 60750 Group. In 2011 the vehicle came under the care of the APT-E Conservation and Support Group