I commuted from Peterborough to Kings Cross for years in the early 1990s. It was lovingly known as cattle class since by the time the train reached PB it was standing room only, unless you fancied sitting in Coach B (the smoker) or standing in the buffet.
Coming back after a night on the lash in London, the after midnight trains were called the "divorce trains". There were 2 as I remember, one at 1.40am and one at 3.40am. You were in a fair amount of poo if you got the 1.40, after that it was best just to stay in a hotel. (For a few days!)