The first standardised railway carriage design built by British Railways, the Mark 1 coach introduced in 1951 could be found across Britain's railway network and continued to be produced until 1963, and even later in the form of multiple units and non-passenger stock. Along with being widely deployed, Mk1 coaches were built in various places including Derby, Doncaster, Eastleigh, Swindon, Wolverton and York.

Most Mk1 coaches had 63ft 5in long underframes with 64ft 6in long bodies, although some were built shorter to be used on tighter curves where large overhangs would otherwise have prohibited running. In 1977 a reduction in the number of fatalities on British railways since 1955 was attributed to the introduction of the Mk1 coaches due to their steel build, strong underframe, and buckeye couplings making them far safer in the event of an accident.

Mk1 coaches started to be withdrawn from widescale service in the 1990s, although in some regions, particularly in the south, Mk1 base multiple units continued to be used well into the 2000s. Network rail continue to use modified Mk1 coaches for various departmental duties and rail tour operators continue to use Mk1 coaches on specially organised services.

The Mk1 RB is a Mk1 Restaurant Buffet coach containing a kitchen and a serving buffet counter. As well as these features the coach would also feature seating, usually with a capacity of 23 passengers. The first phase of building British Railways' Mk1 catering vehicles followed the traditional pattern of dining that had been catered for since Edwardian times, with large Kitchen Cars preparing multiple course dining for consumption in both First and Third Class Dining Cars. However, during the early 1950s it became apparent that social patterns regarding rail travel catering were changing, a direct consequence of WWII attitudes towards dining.

The catering department of British Railways was experiencing a demand from travellers for cheaper and lighter meals and was seeing an increase in social drinking that was not related to dining. This change in dining patterns meant that the use of a Buffet vehicle, rather than a full Kitchen Car/Dining Car combination, was sometimes a better option and the third phase 1957-62 Mk.1 building programme provided many of BR's vehicles with buffet facilities, not just in addition to full meal provision, but also replacing it. Propane gas units were used for gas cooking, reducing the reliance on electric power which, in turn, allowed for a smaller dynamo and battery.