£113 is the off-peak single, I presume?
If you intend to go back the other way by train in the next 3 months (even if it's only to somewhere only in roughly the same direction, even somewhere like Newcastle), you may be better off buying both tickets at the same time.
If not, you could save some money by buying a £55.20 off-peak single as well as a £17 advance ticket in the other direction for some date in the future (for instance, the 6:05 departure on 1/11 is currently at that price), and simply throwing the second ticket away when you get it.
These tickets can be bought on the Virgin web site, and possibly on some others. Ticket offices can't sell them, though, as far as I know.