Private ownership of wagons dates back as far as the 1850s and subsequently there was a long period when wagons either belonged to railway companies or to private owners. The latter was particularly the case with coal traffic. Coal mines had vast fleets of them and many a local coal merchant had one or two to bring his stock of coal for bagging up. Between these two there were coal factors who traded in coal on a large scale, supplying industry, ports and domestic needs with their own privately owned, or leased, fleet. Whether owned by the mines, factors or local coal merchants, they all carried the livery of their operator and added greatly to the colourfulness of the railways. Most were painted brown (iron), black (carbon) or grey (lead), as other pigments faded quickly and meant costly repaints.

At one time the 7-plank wagon was the most numerous type of wagon on Britain's rail network and almost all were involved in the coal business. Indeed, 75% of all privately owned wagons were operated by colliery companies. They were privately owned up until the Second World War, when they were pooled for the war effort and, with the nationalisation of the mines in 1947 and railways in 1948, they became state owned. A considerable number of them were acquired by the National Coal Board for internal use. Those that passed to British Railways were repainted in grey and given a new fleet number with a 'P' prefix.