Railways Act 1921 in the context of "History of rail transport in Great Britain"

The East Coast Main Line (ECML) is a 393-mile-long (632 km) electrified railway between its northern terminus at Edinburgh Waverley and southern terminus at London King's Cross. Peterborough, Doncaster, York, Darlington, Durham and Newcastle are on the line, which is a key transport artery on the eastern side of Great Britain running broadly parallel to the A1 road. The main line acts as a 'spine' for several diverging branches, serving destinations such as Cambridge, Leeds, Hull, Sunderland and Lincoln, all with direct services to London. In addition, a few ECML services extend beyond Edinburgh to serve other Scottish destinations, such as Stirling, Inverness, Dundee, or Aberdeen.

The line was built during the 1840s by three railway companies, the North British Railway, the North Eastern Railway, and the Great Northern Railway. In 1923, the Railways Act 1921 led to their amalgamation to form the London and North Eastern Railway (LNER) and the line became its primary route. The LNER competed with the London, Midland and Scottish Railway (LMS) for long-distance passenger traffic between London and Scotland. The LNER's chief mechanical engineer Nigel Gresley designed iconic Pacific steam locomotives including Flying Scotsman and Mallard, the latter of which achieved a world record speed for a steam locomotive, 126 mph (203 km/h) on the Grantham-to-Peterborough section on 3 July 1938.

The North Eastern Railway (NER) was an English railway company. It was incorporated in 1854 by the combination of several existing railway companies. Later, it was amalgamated with other railways to form the London and North Eastern Railway at the Grouping in 1923. Its main line survives to the present day as part of the East Coast Main Line between London and Edinburgh.

Unlike many other pre-Grouping companies the NER had a relatively compact territory, in which it had a near monopoly. That district extended through Yorkshire, County Durham and Northumberland, with outposts in Westmorland and Cumberland. The only company penetrating its territory was the Hull & Barnsley, which it absorbed shortly before the main grouping. The NER's main line formed the middle link on the Anglo-Scottish "East Coast Main Line" between London and Edinburgh, joining the Great Northern Railway near Doncaster and the North British Railway at Berwick-upon-Tweed.

The London and North Eastern Railway (LNER) was the second largest (after LMS) of the "Big Four" railway companies created by the Railways Act 1921 in Britain. It operated from 1 January 1923 until nationalisation on 1 January 1948. At that time, it was divided into the new British Railways' Eastern Region, North Eastern Region, and partially the Scottish Region.

The London, Midland and Scottish Railway (LMS) was a British railway company. It was formed on 1 January 1923 under the Railways Act 1921, which required the grouping of over 120 separate railways into four. The companies merged into the LMS included the London and North Western Railway, the Midland Railway, the Lancashire and Yorkshire Railway (which had previously merged with the London and North Western Railway on 1 January 1922), several Scottish railway companies (including the Caledonian Railway), and numerous other, smaller ventures.

Besides being the world's largest transport organisation, the company was also the largest commercial enterprise in the British Empire and the United Kingdom's second largest employer, after the Post Office.

The Mersey Railway was the passenger railway connecting the communities of Liverpool and Birkenhead, England. It is currently a part of the Merseyrail network. It was extended further into the Wirral Peninsula, which lies on the opposite bank of the River Mersey to Liverpool. Both sides of the river were connected via the Mersey Railway Tunnel. The railway opened in 1886 with four stations using steam locomotives hauling unheated wooden carriages; in the next six years the line was extended with the opening of three more stations. Using the first tunnel under the Mersey, the line is the world's oldest underground railway outside London.

Because the steam locomotives created a polluted atmosphere in the tunnel despite the forced ventilation system, many passengers reverted back to using the river ferries making the railway bankrupt by 1900. Recovery came after the railway adopted electric traction in 1903. The Mersey Railway remained independent after the railway grouping of 1923, although it became closely integrated with the electric train services operated by the London, Midland and Scottish Railway over the former Wirral Railway routes after 1938. The Mersey Railway was nationalised, along with most other British railway companies, in 1948.

The Midland Railway (MR) was a railway company in the United Kingdom from 1844. The Midland was one of the largest railway companies in Britain in the early 20th century, and the largest employer in Derby, where it had its headquarters. It amalgamated with several other railways to create the London, Midland and Scottish Railway at grouping in 1923.

The Midland had a large network of lines emanating from Derby, stretching to London St Pancras, Manchester, Carlisle, Birmingham, and Bristol. It expanded as much through acquisitions as by building its own lines. It also operated ships from Heysham in Lancashire to Douglas and Belfast. A large amount of the Midland's infrastructure remains in use and visible, such as the Midland Main Line and the Settle–Carlisle line, and some of its railway hotels still bear the name Midland Hotel.

The Great Western Railway (GWR) was a British railway company that linked London with the southwest, west and West Midlands of England and most of Wales. It was founded in 1833, received its enabling act of Parliament on 31 August 1835 and ran its first trains in 1838 with the initial route completed between London and Bristol in 1841. It was engineered by Isambard Kingdom Brunel, who chose a broad gauge of 7 ft (2,134 mm)—later slightly widened to 7 ft 1⁄4 in (2,140 mm)—but, from 1854, a series of amalgamations saw it also operate 4 ft 8+1⁄2 in (1,435 mm) standard-gauge trains; the last broad-gauge services were operated in 1892.

The GWR was the only company to keep its identity through the Railways Act 1921, which amalgamated it with the remaining independent railways within its territory, and it was finally merged at the end of 1947 when it was nationalised and became the Western Region of British Railways.

The Lancashire and Yorkshire Railway (L&YR) was a major British railway company before the 1923 Grouping. It was incorporated in 1847 from an amalgamation of several existing railways. It was the third-largest railway system based in northern England (after the Midland and North Eastern Railways).

The intensity of its service was reflected in the 1,650 locomotives it owned – it was by far the most densely trafficked system in the British Isles with more locomotives per mile than any other company – and that one third of its 738 signal boxes controlled junctions averaging one every 3+1⁄2 miles (6 km). No two adjacent stations were more than 5+1⁄2 miles (9 km) apart and its 1,904 passenger services occupied 57 pages in Bradshaw, a number exceeded only by the Great Western Railway, the London and North Western Railway, and the Midland Railway. It was the first mainline railway to introduce electrification of some of its lines, and it also ran steamboat services across the Irish Sea and North Sea, being a bigger shipowner than any other British railway company.