You are responsible for ensuring that you purchase a ticket or obtain a Promise to Pay Notice that is valid for your entire journey before travelling, otherwise you may have to pay a Penalty Fare.
Northern is responsible for ensuring that the facility to purchase a ticket or Promise to Pay Notice is available. If there are no ticket selling facilities available at the station where you board, you will be able to purchase a full range of tickets from the conductor.
In these circumstances we recommended you board the rear carriage in order to purchase your tickets from the conductor.