article: List of railway companies involved in the 1923 grouping
links: Great Eastern Railway Railways Act 1921 London, Brighton and South Coast Railway London and North Western Railway Southern Railway (Great Britain) Great Western Railway London and North Eastern Railway North Eastern Railway (UK) South Eastern and Chatham Railway London, Midland and Scottish Railway Great Northern Railway (Great Britain) Great Central Railway Midland Railway London, Chatham and Dover Railway London and South Western Railway Big Four British railway companies Lancashire and Yorkshire Railway South Eastern Railway (UK) Caledonian Railway Cambrian Railways Northern Ireland