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█ Great Western • █ London Midland & Scottish • █ London & North Eastern • █ Southern

GWR constituents: Great Western Railway • Cambrian Railways • Taff Vale Railway
Barry Railway • Rhymney Railway • (Full list)
LNER constituents: Great Central • Great Eastern • Great Northern • Great North of Scotland
Hull & Barnsley • North British • North Eastern • (Full list)
LMS constituents: Caledonian • Furness • Glasgow & South Western • Highland
Lancashire & Yorkshire • London and North Western • Midland • North Staffordshire • (Full list)
SR constituents: London and South Western Railway • London, Brighton and South Coast Railway
South Eastern Railway • London, Chatham and Dover Railway • (Full list)

See also: History of rail transport in Great Britain 1923 - 1947 • List of companies involved in the grouping