The Southern Railway was one of the "Big Four" railway companies set up after the 1923 Grouping. This list sets out the constituents of the Company.

Constituent companies

• The London and South Western Railway (LSWR) route mileage 1020 miles (1632km)
• The London, Brighton and South Coast Railway (LBSCR) 457.25 miles (736km)
• The combined systems of the South Eastern Railway and the London, Chatham and Dover Railway, under the South Eastern & Chatham Railways' Managing Committee (SECR) 637.75 miles (1026km). These concerns had amalgamated under a Managing Committee on 1 January 1922.

The London and South Western Railway (L&SWR) was a railway company in the United Kingdom from 1840 to 1923. ... Early days The London, Brighton, and South Coast Railway or LB&SCR was a railway company in the United Kingdom from 1846 to 1923. ... The London and Greenwich Railway (LGR), together with the Canterbury and Whitstable Railway (CWR) in East Kent were the earliest railways to serve the then county of Kent: eventually both became parts of the South Eastern Railway (SER). ... Crest of the LCDR on the first Blackfriars Railway Bridge The London, Chatham and Dover Railway was a railway company that operated in south-eastern England between 1858 and 1923 before grouping with three other companies to form the Southern Railway. ... Coat of Arms. ...

Subsidiary companies

Independently operated lines

• Freshwater, Yarmouth and Newport (Isle of Wight) Railway 12 miles (19km)
• Isle of Wight Railway 15.25 miles (24km)
• Isle of Wight Central Railway 28.5 miles (46km)
• Bere Alston and Callington section of the Plymouth, Devonport and South Western Junction Railway 9.75 miles (16km)

Non-working companies

• Originally leased to or worked by LSWR
  • Bridgewater Railway 7.25 miles (12km)
  • Lee-on-the-Solent Railway 3 miles (5km)
  • North Cornwall Railway 52.5 miles (84km)
  • Plymouth and Dartmoor Railway (portion used by LSWR) 2.25 miles (4km)
  • Plymouth, Devonport and South Western Junction Railway (except Bere Alston and Callington section as above) 19.5 miles (31km)
  • Sidmouth Railway 8.25 miles (13km)
• Originally leased to or worked by LBSCR
  • Brighton and Dyke Railway 4.75 miles (8km)
  • Hayling Railway 5 miles (8km)

Originally leased to or worked by SER or LCDR

• London and Greenwich Railway 3.75 miles (6km)
• Mid Kent Railway (Bromley to St Mary Cray) 2.5 miles (4km)

Other railways The London and Greenwich Railway (LGR), together with the Canterbury and Whitstable Railway (CWR) in East Kent were the earliest railways to serve the then county of Kent: eventually both became parts of the South Eastern Railway (SER). ... The London and Greenwich Railway (LGR), together with the Canterbury and Whitstable Railway (CWR) in East Kent were the earliest railways to serve the then county of Kent: eventually both became parts of the South Eastern Railway (SER). ...

• Victoria Station and Pimlico Railway (in which the Great Western Railway and the London and South Western Railway were also parties)
• Lynton & Barnstaple Railway: not covered by the Railways Act 1921, but absorbed by the LSWR. 19.25 miles (31km)

Bristol Temple Meads railway station, the original terminus at Bristol. ... The London and South Western Railway (L&SWR) was a railway company in the United Kingdom from 1840 to 1923. ... The Lynton & Barnstaple Railway was a narrow-gauge railway through Exmoor in North Devon, England which operated between 1898 and 1935. ...

Joint companies

• In 1923, now comprised wholly in the SR:
  • Croydon & Oxted Railway 12.5 miles (20km (was SE&CR))
  • Dover & Deal Railway 8.5 miles (14km) (was SE&CR)
  • Epsom & Leatherhead Railway 3.75 miles (6km) (was LBSCR/LSWR joint)
  • Portsmouth & Ryde Railway (the ferry) 8.5 miles (14km) (was LBSCR/LSWR joint)
  • Tooting, Merton & Wimbledon Railway 5.75 miles (9km) (was SE&CR)
  • Woodside & South Croydon Railway 2.5 miles (4km) (was LBSCR/ SE&CR joint)
• In 1923, in association with other companies:
  • East London Railway 5 miles (8km) (1/3 share with London and North Eastern Railway and Metropolitan Railway)
  • Easton & Church Hope Railway 3.5 miles (6km) (jointly with Great Western Railway (GWR))
  • Somerset and Dorset Joint Railway 105 miles (168km) (with London, Midland and Scottish Railway (LMSR))
  • West London Extension Railway 5.25 miles (8km) (shares with GWR and LMSR)
  • Weymouth & Portland Railway 5.5 miles (9km) (jointly with GWR)

The information in this article taken from the Railway Magazine for February 1923 Crossing the Thames The River Thames has always formed a barrier to any links between the north and south of London, particularly to the eastern side where communication to the routes to the Continent are concerned. ... The London and North Eastern Railway or LNER was the second-largest of the Big Four railway companies created by the Railways Act 1921 in Britain. ... The Metropolitan Line is a line of the London Underground. ... Bristol Temple Meads railway station, the original terminus at Bristol. ... The Somerset and Dorset Joint Railway (S&DJR) was an English railway company jointly owned by the Midland Railway and the London and South Western Railway. ... The London, Midland and Scottish Railway (LMS1) was a British railway company. ...

See also

List of railway companies involved in the 1923 grouping Under the Railways Act 1921 the majority of the railway companies in Great Britain (and few in Northern Ireland) were grouped into four main companies, often termed the Big Four: the grouping took effect from 1 January 1923. ...