What were the 'Big Four' railway companies in the UK before nationalisation
The Big Four were London, Midland and Scotland (LMS), London and North Eastern Railway (LNER), Great Western Railway (GWR) and Southern Railway (SR)
Instruction: What were the 'Big Four' railway companies in the UK before nationalisation
Context: 
Response: The Big Four were London, Midland and Scotland (LMS), London and North Eastern Railway (LNER), Great Western Railway (GWR) and Southern Railway (SR)