You haven't answered how barriers would stop what I said.
If the person has to pass the barriers in order to get to station facilities (which is the case in many many stations), then surely someone who wants to end their journey early or break their journey against their tickets restrictions could just claim they are going to use the station facilities? The only way you could "catch" then is if you then see them leaving the station. Something that would not likely be possible when the station is busy, or if the station is unmanned.
The ticket then becomes invalid. They would not be allowed to pass the barrier until they have been excessed to the full single fare or indeed cautioned and reported under S5.
Scenario for you.
Unnamed station former BR London Division.
Passenger arrives off a train which started from London and presents themselves at the barrier with a ticket from London to the station in question.
The station however is shown as a stop to "pick up only". That is the station is not available for alighting passengers.
Passenger is refused exit and is charged the single fare from Euston to the first calling point of the train. This is on the basis that the ticket was not valid on that service as the train was not calling. Covered in the NCoC.
A good example of terminating short is the megatrain ticket. This expressly prohibits the journey being ended short and prohibits a break of journey except to use connecting services.
If a person presents themselves at a barrier with one of these or similar, then the excess regulations are quite clear. Its the full fare from origin. Indeed it could well be argued that the correct action would be a S5 caution, and it would be if the right question was answered in the honest manner. We have however documented evidence on this site of at least one person proposing to do so in order to avoid paying the higher fare to the intermediate station.
Normally I wouldn't say anything personal such as this but Old Timer, your views are draconian and extreme, this is the railway, not HM Prison Service.
I am merely pointing out the correct position and the various conditions of carriage.
People enter into an agreement with the Railway when they buy a ticket. I have never met anyone who was dragged off the street under gunpoint and forced to buy a ticket and travel.
Passengers expect the Railway to honour their committments why should it be that the passengers committments are a one way street when it does not suit ?
Why is it extreme to point out such things ?