I fully agree that people who travel on an earlier or later train without seking an endorsement at the booking office or the permission of the guard, should be penalised. However, in the context of this thread, I don't think it is wrong if someone asks if they can travel earlier. I was asked a lot at Reading, usually when people overestimated the time that it would take to get through Heathrow Airport and on to Reading. I always told them they had three options. Buy a new ticket, have a word with the guard, or go and get something to eat or drink at Gregory's Cafe (they should have given me commission!). I always told them the price of a new ticket and explained that if they just got on the early train that is what they may have to pay on board.