In Scotland the following major companies were merged;
Caledonian
Railway
Glasgow
and South Western Railway
Highland Railway
In England the following major companies were merged;
London
and North Western Railway
Midland Railway
Besides these many other companies were merged into what became known as the LMS.
The LMS re-organised the management of the companies into a single management structure which was a difficult slow but ultimately rewarding process. The combined company was managed from London. The geographical nature of the lines led to some areas which had no competition but multiple lines owned by the LMS. Examples include the Clyde Coast, Ayrshire and approaches to the South of Carlisle. In Ayrshire the led to the run-down of the Caledonian Railway's Lanarkshire and Ayrshire Railway in preference to the former Glasgow and South Western Railway.
In 1948 the four large companies were merged to form British Railways - a nationalised railway company.