The following is a list of constituents of British Railways. British Railways (BR) was formed by nationalisation on 1 January 1948 in accordance with the Transport Act 1947

Transport Act 1947

The Transport Act 1947 is an Act of the Parliament of the United Kingdom. Under it the railways, long-distance road haulage and various other types of transport were acquired by the state and handed over to a new British Transport Commission for operation...

. It had four major constituents, but there were a number of joint lines between these, and additionally some light railways

Light Railways

Light Railways is a magazine produced by the Light Railway Research Society of Australia . The subtitle is "Australia's Magazine of Industrial and Narrow Gauge Railways"....

 were taken into the fold. Even then, some light railways were not nationalised.

Major constituents

The major constituents (the "Big Four

Big Four British railway companies

The Big Four was a name used to describe the four largest railway companies in the United Kingdom in the period 1923-1947. The name was coined by the Railway Magazine in its issue of February 1923: "The Big Four of the New Railway Era".The Big Four were:...

") were:

• Great Western Railway
  Great Western Railway
  The Great Western Railway was a British railway company that linked London with the south-west and west of England and most of Wales. It was founded in 1833, received its enabling Act of Parliament in 1835 and ran its first trains in 1838...
  
   (GWR)
• London Midland and Scottish Railway (LMS)
• London and North Eastern Railway
  London and North Eastern Railway
  The London and North Eastern Railway was the second-largest of the "Big Four" railway companies created by the Railways Act 1921 in Britain...
  
   (LNER)
• Southern Railway
  Southern Railway (Great Britain)
  The Southern Railway was a British railway company established in the 1923 Grouping. It linked London with the Channel ports, South West England, South coast resorts and Kent...
  
   (SR)

Joint railways

Joint railways between the four major constituents (and others) were:

• Axholme Joint Railway Committee (1/2 LMS, 1/2 LNER)
• Cheshire Lines Committee
  Cheshire Lines Committee
  The Cheshire Lines Committee was the second largest joint railway in Great Britain, with 143 route miles. Despite its name, approximately 55% of its system was in Lancashire. In its publicity material it was often styled as the Cheshire Lines Railway...
  
   (2/3 LNER, 1/3 LMS)
• Dumbarton and Balloch Joint Railway (1/2 LMS, 1/2 LNER)
• Dundee and Arbroath Joint Railway (1/2 LMS, 1/2 LNER)
• East London Railway Joint Committee (1/6 LNER, 1/2 SR, 1/3 London Transport)
• Forth Bridge Railway Company (2/3 LNER, 1/3 LMS)
• Grangemouth Branch Railway
• Great Central and Midland Joint Committee (1/2 LMS, 1/2 LNER)
• Great Central and North Staffordshire Joint Committee (1/2 LMS, 1/2 LNER)
• Great Central and North Western Railways Joint Committee (1/2 LMS, 1/2 LNER)
• Great Central, Hull and Barnsley and Midland Committee (2/3 LNER, 1/3 LMS)
• Great Northern and London and North Western Joint Committee (1/2 LMS, 1/2 LNER)
• Great Western and Great Central Railways Joint Committee
  Great Western and Great Central Joint Railway
  The Great Western and Great Central Joint Railway was a joint venture supported by the Great Western Railway and Great Central Railway and run by the Great Western and Great Central Joint Committee. The original arrangement was agreed between the two companies in September 1898...
  
   (1/2 GWR, 1/2 LNER)
• Great Western and Great Central (Banbury Junction Railway) Joint Committee (1/2 GWR, 1/2 LNER)
• Halifax and Ovenden Joint Committee
• Halifax High Level Joint Committee
• London, Midland and Scottish and Great Western Railways Joint Committee (1/2 GWR, 1/2 LMS)
• Manchester, South Junction and Altrincham Railway Company (1/2 LMS, 1/2 LNER)
• Metropolitan and Great Central Joint Committee (1/2 LNER, 1/2 London Transport)
• Midland and North Eastern Railway Companies Committee (1/2 LMS, 1/2 LNER)
• Mid-Nottinghamshire Joint Railway Committee (1/2 LMS, 1/2 LNER)
• Midland and Great Northern Joint Railway
  Midland and Great Northern Joint Railway
  The Midland and Great Northern Joint Railway, was a joint railway owned by the Midland Railway and the Great Northern Railway in eastern England, affectionately known as the 'Muddle and Get Nowhere' to generations of passengers, enthusiasts, and other users.The main line ran from Peterborough to...
  
   (1/2 LMS, 1/2 LNER)
• Norfolk and Suffolk Joint Railways Committee (1/2 LMS, 1/2 LNER)
• Oldham, Ashton-under-Lyne and Guide Bridge Junction Railway Company
• Otley and Ilkley Joint Line Committee (1/2 LMS, 1/2 LNER)
• Somerset and Dorset Joint Railway
  Somerset and Dorset Joint Railway
  The Somerset & Dorset Joint Railway – almost always referred to as "the S&D" – was an English railway line connecting Bath in north east Somerset and Bournemouth now in south east Dorset but then in Hampshire...
  
   (1/2 SR, 1/2 LMS)
• South Yorkshire Joint Line Committee (1/2 LMS, 1/2 LNER)
• Watford Joint Railway Committee (1/2 LNER, 1/2 London Transport)

Minor railways and Light railways

• East Kent Light Railway
  East Kent Light Railway
  The East Kent Light Railway was part of the Colonel Stephens group of cheaply built rural light railways in England. Holman Fred Stephens was engineer from its inception, subsequently becoming director and manager...
  
  
• Kent and East Sussex Railway
  Kent and East Sussex Railway
  The Kent & East Sussex Railway refers to both an historical private railway company in Kent and Sussex in England, as well as a heritage railway currently running on part of the route of the historical company.-Historical Company:-Background:...
  
  
• Mersey Railway
  Mersey Railway
  The Mersey Railway connected Liverpool and Birkenhead, England, via the Mersey Railway Tunnel under the River Mersey. Opened in 1886, it was the second oldest urban underground railway network in the world. The railway contained the first tunnel built under the River Mersey. It was constructed by...
  
  
• North Devon and Cornwall Junction Light Railway
• Shropshire and Montgomeryshire Railway (1950)

Irish railways

Irish railways owned by the LMS (the Northern Counties Committee

Northern Counties Committee

The Northern Counties Committee was a railway that served the north-east of Ireland. It was built to Irish gauge but later acquired a number of narrow gauge lines...

 lines) were also acquired but were quickly sold on to the Government of Northern Ireland

Executive Committee of the Privy Council of Northern Ireland

The Executive Committee or the Executive Committee of the Privy Council of Northern Ireland was the government of Northern Ireland created under the Government of Ireland Act 1920. Generally known as either the Cabinet or the Government, the Executive Committee existed from 1922 to 1972...

.