These carriages were initially ordered by the London Midland Region of BR to D17 with B1 bogies (kit B18K). 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.
From 1969 all but three (324, 325, 332) were rebuilt to D26 or D28, converting them to restaurant/buffet cars, and with Commonwealth bogies if not already so upgraded. For D26, the external appearance was unchanged but internally half of the seats were removed and replaced with a standing area for the buffet. One of the unrebuilt coaches (M325) was included in the Royal Train, renumbered to 2907. D28 were changed similarly, but a further internal arrangement of the shelving and display area required the window to the right of the intermediate door on the kitchen side of the coaches to be plated over, thus altering the appearance of this side.