You might try Ancestry's Railway Employment Records collection. Quote from their website about the collection:
What is included?
All of the railways included in this database were once private companies that later came under authority of the British Transport Commission with the 1947 Transport Act. The collection features selected records from the following companies:
RAIL226: Great Central Railway Company
RAIL264: Great Western Railway Company
RAIL397: London and North Eastern Railway Company
RAIL410: London and North Western Railway Company
RAIL411: London and South Western Railway Company
RAIL414: London, Brighton and South Coast Railway
RAIL415: London, Chatham and Dover Railway Company (formerly the East Kent Railway)
RAIL426: London, Midland and Scottish Railway Company
RAIL463: Manchester, Sheffield and Lincolnshire Railway Company
RAIL491: Midland Railway Company
RAIL1156: Special Collections: Retired Railway Officers' Society
Approximately 50% of the books cover the Great Western Railway, while the books covering the London and North Western Railway are more dense with records. Most records are prior to 1949, though some date later.