Reminds me of a friend on a Newcastle - London via Durham train ticket. It was an off-peak ticket, so cheaper. At the last minute he found himself staying with a friend in Durham, so he arrived to board the train in Durham. Not allowed because the ticket had to be validated in Newcastle
This can even be a problem if you get off the train EARLIER than the specified destination. You can be charged with fare evasion if getting off the train at that station would be more expensive than staying on until the station given on your ticket.