The London, Midland and Scottish Railway (LMS) was a British railway company. It was formed on 1 January 1923 under the Railways Act of 1921, which required the grouping of over 120 separate railway companies into just four. The companies merged into the LMS included the London and North Western Railway, Midland Railway, several Scottish railway companies (including the Caledonian Railway), and numerous other, smaller ventures.The resulting company was an unwieldy construction, with numerous interests other than railway operations. Besides being the world’s largest transport organisation, it was also the largest commercial undertaking in the British Empire and the United Kingdom’s second largest employer, after the Post Office. The LMS also claimed to be the largest joint stock organisation in the world.The LMS was the largest of the Big Four railway companies and the only one to operate in all parts of the United Kingdom: England, Northern Ireland, Scotland and Wales.