I know this has been asked before but I cant find the answer. In a Penalty Fare area can you choose to travel via the more expensive route and upgrade on the train or must the upgrade be done before boarding. I will be boarding at Poole travelling with a ticket routed Dorchester but may need to instead go via Salisbury if running late and won't have time to go to the booking office. There are off peak return tickets routed both ways and neither are operator specific.