Here is a hypothetical situation. An advance fare from point A to point C, going through, and stopping at point B, is significantly cheaper than one between point A and point B on the same train. The NRCoT are very clear that you can't end your journey and will be charged the difference in the fare between what you have paid for your ticket and the cheapest fare on the day if you do end your journey at point B. However on every train there is a notice that if you feel unwell (just before point B say) you should alight there. The Byelaws say that you must comply with such notices, which I would guess means that the TOC shouldn't ask you to pay for the difference in the fares. Opinions please?