I am travelling tomorrow from Porthmadog to Gatwick Airport. The ticket to cover my journey will be an Off-Peak return, costing £61.40 with a railcard. I have a single Rail Travel Voucher valid for slightly more than this, which I wish to use as this is the only journey I am likely to be making that will cost anywhere near this. How do I buy my ticket? There is neither booking office nor ticket machine at Porthmadog. I am unable to buy on-line, as I am using an RTV for payment. Even if I were not, I would be unable to buy an e or m-ticket, as these can't be used for cross-London journeys. The guard on the train will be unable to sell me a ticket, as their new ticket machines issue paper-roll tickets which likewise cannot be issued for cross-London journeys. As I am joining the train at a station that has no ticketing facilities, I understand that I am entitled to board the train without a ticket. However, what happens if the guard is then unable to sell me the ticket for the journey I am making? Later on in my journey, the train will be passing through a Penalty Fare Zone.