These carriages were initially ordered by the London Midland Region of BR with B1 bogies. They were built in two batches, the first four coaches by BRCW, the remainder being shared between the BR works at Ashford and Swindon. They were unique in BR catering coach designs in having passenger entrance doors instead of access only via the gangways from adjacent vehicles.
Most if not all would have been upgraded with Commonwealth bogies (kit B18AK), as shown in the photos. From 1969 all but three (324, 325, 332) were rebuilt to D26 or D28, converting them to restaurant/buffet cars (also kit B18AK).