The 'Conflat A' was a post-war Swindon design and the first 400 were built at Swindon and Wolverton. Over the next ten years, 200,000 of them were built, most of them during the BR era. There is little difference between the GWR and BR versions. As road transport developed in the 1930s, containers were introduced to the railways in order to compete. Post World War 2, there was a big drive to promote container traffic by the four railway companies. Each had a door-to-door service, for house moving, using their own road vehicles and flat railway wagons to achieve this.

The containers were restricted in design as to what would fit the vehicles and the standard loading gauge of the railways. Containers had their own number codes but, under British Railways, they became known as 'B' type and variations were acknowledge by a second letter, in this case a 'D' making it a 'BD' container. BDs were general merchandise containers and had side doors as well as doors at one end. They became the most widely used container design of their day and had a capacity of 720 cubic feet and a loading limit of four tons. A recent addition to the Bachmann range is 37-951C consisting of 'Conflat A' B709007 carrying a BR red BD container numbered BD50311B.