Between WWI and WWII, the Great Western Railway developed the use of containers that could be packed and locked at a client's premises, taken by lorry to a station, then carried by train and again by lorry to the final destination. Using these containers, they offered a door-to-door removals service, providing a team to pack the furniture, and a discount on fares to the destination.^[1] Some containers could carry up to 72 bicycles.^[2] Insulated containers, cooled by boxes of ice, were used to transport flower bulbs and other perishable items.^[3]

Originally such containers were carried on general-purpose flat trucks and wagons, but from 1931 the GWR built or converted a number of special purpose flat-bedded wagons, provided with chains for securing the load. They were called by the telegraphic code Conflat, and most of them were fitted with vacuum brakes.^[4][5]

In 1930 the railway introduced 100 containers primarily for building materials.^[6]

• External size: 7 ft 4 in × 4 ft 4+1⁄2 in (2,235 mm × 1,334 mm) height 1 ft 6+1⁄2 in (470 mm)
• Internal size: 7 ft 0 in × 4 ft 0 in (2,134 mm × 1,219 mm) height 1 ft 3 in (381 mm)
• Capacity: 1 long ton 10 cwt (3,400 lb or 1.5 t), tare weight 6 long cwt (700 lb or 300 kg)