In 1947 the newly formed British Railways saw the need to standardise their passenger stock. These coaches would be constructed from 1951 to 1963 with only one significant change made during this time, a swapping of bogies in the last gasps of the Mark 1s build cycle. The Mark 1 coach as it would be designated was designed to be a go anywhere, do anything coach utilising the best features from each of the big four coaches the company had inherited.