British Railways Mark 1 was the family designation for the first standardised designs of railway carriages built by British Railways. Following nationalisation in 1948, BR had continued to build carriages to the designs of the "Big Four" companies (the Great Western

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...

, Southern, London Midland and Scottish and London and North Eastern

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...

 railways), and the Mark 1 was intended to be the standard carriage design for use across all lines, incorporating the best features of each of the former companies' designs.