They were introduced in two batches . The first were in 1938 , by the London , Midland and Scottish Railway ( LMS ) with a further batch ( built to a similar design ) in 1956 by the then nationalised British Railways ( BR ) .
They were introduced in two batches -- in 1938 by the London , Midland and Scottish Railway ( LMS ) with a further batch ( built to a similar design ) in 1956 by the then nationalised British Railways ( BR ) .