The importance of Britains railways was greatly emphasised during the First World War, when British railways were taken over by the Government under the Regulation of Forces Act, 1871. The railways remained under Government control until August 1921.
In 1921, Royal Assent was given to the Railways Bill which included provisions for grouping. This resulted in the formation of the `big four' British main-line railway companies, ie. Great Western Railway (the only one already existing), London Midland & Scottish, London North Eastern Railway and Southern Railway.
It was 1 January 1923 that 123 seperate railway companies were amalgamated and absorbed into four group companies.
These railway companies operated until nationalisation on 1 January 1948.