During the First World War the government had taken control of the railways to co-ordinate the war effort. After the war ended it was decided that the railway companies could not competitively return to their prior state, and so the 120 existing railway companies were combined into four companies, which became known as the ‘Big Four’’. The London Midland and Scottish Railway, also known as the LMS, was founded on 1 January 1923. The London and North Western Railway (LNWR), Midland Railway (MR), Lancashire and Yorkshire Railway (LYR), North Staffordshire Railway (NSR), Highland Railway (HR), Furness Railway (FR), Glasgow and South Western Railway (G&SWR) and Caledonian Railway (CR) were merged. These eight large constituent companies were joined by 27 other smaller subsidiary railways. The LMS covered the Western half of the country, stretching from the London and the Midlands, through Yorkshire, Lancashire, and up to Scotland. In all the LMS had a total of 7,790 miles of track, which made it the largest railway of the Big Four. The London termini of the LMS were St. Pancras and Euston stations and it had works at Crewe, Horwich, Wolverton and Derby amongst other locations. In 1934 the LMS moved into a new headquarters at Euston House on Seymour Street (later renamed Eversholt Street) in London. Charles Napier Lawrence, 1st Baron Lawrence of Kingsgate was the first appointed chairman of LMS, he had previously been the chairman of the LNWR between 1921-1923. He was chairman of the LMS for one year, and was succeeded by Sir Guy Granet. The management structure was headed by a chairman and a deputy chairman, there was a board of directors that had initially had 20 members, made of men who previously worked for the constituent companies. The first General Manager was Arthur Watson from the LYR. There was a Deputy General Manager for Scotland, a post first held by D.A. Matthieson, formerly of the CR. J.H. Follows, from the Midland Railway, was the first Chief General Superintendent and S.H. Hunt, formerly of the LNWR, was the first Chief Goods Manager. The post of Chief Engineer was initially held by E.F.C. Trench, formerly employed by the LNWR. The first Chief Mechanical Engineer was G. Hughes from the LYR and his deputy was Sir Henry Fowler, from the Midland Railway. The management structure was re-organised from January 1926 and an Executive was set up, Sir Josiah Stamp was the first President of the Executive. From January 1927 four Vice-Presidents were appointed to replace the general managers on the Executive committee. The line was divided up for operational management into three geographical divisions, which were called Western, Midland and Northern. Each division was overseen by a General Superintendent who reported to the Chief General Superintendent. The main line of the LMS ran from London Euston to Wick over 729 miles. The LMS ran a number of joint railways with the London & North Eastern Railway and the Southern Railway. It ran the Cheshire Lines Committee, the Midland and Great Northern line between Peterborough, the Norwich and Lowestoft and the Manchester, South Junction and Altrincham suburban line with the London & North Eastern Railway. It also joined forces with the Southern Railway to run the Somerset and Dorset line between Bath, Burnham and Bournemouth. The LMS undertook a limited programme of electrification, mainly focusing on suburban lines in London and Manchester. The LMS owned many hotels, including the Queen’s Hotel in Leeds and the iconic Art Deco Midland Hotel at Morecombe Bay. The LMS also ran passenger steamers from Holyhead, Heysham and Stranraer over the Irish Sea to Northern Ireland and the Republic of Ireland. Following the 1947 Transport Act which nationalised the railways, the concerns of the LMS were taken over by the Railway Executive as part of the British Transport Committee. Within the Railway Executive, British Rail: London Midland Region assumed responsibility for the LMS’s former area of operations.

The London & North Western Railway Co (LNWR) was established in 1846 following the amalgamation of the London & Birmingham, Manchester & Birmingham and Grand Junction Railways. The new company was the largest joint stock company in Britain, and initially had a network of approximately 350 miles (560 km) connecting London with Birmingham, Crewe, Chester, Liverpool and Manchester. The LNWR continued to expand and by 1868 the company had added links to Oxford, Cambridge, Leeds, Swansea and Cardiff. However, attempts to amalgamate with Midland Railway ended in failure. By 1871 the London & North Western Railway employed 15,000 people. As part of the 1923 Grouping the LNWR became a constituent of the London, Midland and Scottish (LMS) Railway.