Can I combine two "consecutive" tickets on the same journey without leaving the train?

Question

I booked off-peak return tickets from London to Oxford. Unfortunately I mis-tapped in the Trainline app and accidentally bought tickets to Oxford Parkway rather than Oxford (the main station). Parkway is the station directly before it.

I could get a refund on the tickets and buy correct tickets; however, Trainline charges a 10 GBP fee in this case.

I’m wondering whether I could just buy a cheap return ticket Oxford Parkway–Oxford instead, and combine the two legs of the journey (London Marylebone–Oxford Parkway, Oxford Parkway–Oxford … and vice-versa on the return) into one, without having to leave the train (or the station) at Oxford Parkway.

In case that changes anything, the tickets were bought using a Two Together Railcard.

Answer 1

Yes you can do this - as long as the train stops at the intermediate station there is no need to physically get on/off the train. You can buy tickets between any combinations of stations from any station, so you can buy the tickets at London station before leaving.

I've personally done this loads of times, but the relevant section in the conditions of travel is:

14.1. Unless shown below, you may use a combination of two or more Tickets to make a journey provided that the train services you use call at the station(s) where you change from one Ticket to another.

---

However, there may be a cheaper & better option. You could instead an overdistance excess fare, this "changes" your existing ticket. Information on these can be found here (assuming you are at a ticket office before traveling)

a customer travelling beyond the destination of the ticket will be required to pay an Excess fare for the difference in price between the ticket held and the appropriate Single or Return fare, available for immediate travel, for the complete journey from the originating station to the final destination

And for the price:

the difference between the fare paid and the appropriate Return fare for the throughout journey. If cheaper, charge the appropriate Single fare for the extra journey.

Excess fares can only be obtained from staffed ticket office, you cannot purchase them online or from ticket machines. My personal experiences is that you may need a certain level of assertiveness/trial and error to purchase excess fare tickets as they are not commonly issued. You are likely to face an additional problems if your existing ticket is anything but an orange slip of card. Excess fares can be optioned for any ticket type in theory but it posses additional problems as e/m tickets do not have a ticket number - staff usually enter 12345 in my experience but others are unwilling to do so. Note that an excess fare ticket comes as an additional slip of paper, make sure you keep both at all times as it is only valid with the original ticket. In my experience excess fare tickets do not work any ticket barriers, you will likely need to find a member of staff to let you out/in at Oxford. Although your original ticket will work the barriers fine in London. While it will be harder to obtain an excess fare it does mean that your train no longer needs to stop at Oxford Parkway, so you will additionally be able to use the faster GWR trains.

Answer 2

No need to leave train. Just tap out with your other ticket at the exit. As long as you have a valid ticket (or tickets) for the entire length of your journey it doesn't matter.

Answer 3

You can just chance it, I've made the same mistake, explained it at the barrier and they have waved me through. Last time I checked, the price difference is 10p. Caveat Emptor...