Hello,
If you forget your railcard on a trip which involves an outward and return Advance leg, are you able to claim back both, or just one of the legs of the journey?
Please clarify!
Did you forget your railcard and buy a non-discounted ticket?
Or did you forget your railcard, buy a ticket with a railcard discount, and were unable to show the railcard to an inspector?
In the first case, I don't think you can claim anything back, it's your mistake in the first place. If that's what you're asking.
EDIT Given that I now see that you are talking about an advance ticket, I'm guessing that you bought this in advance with a railcard discount, and that when you travelled you didn't have your railcard with you. But what exactly then happened and what are you asking for in terms of a "claim back"?