I^ve had a rummage about here but cannot find a similar question.
Travelling back from Portsmouth
SWMBO▸ realised that she had left the return portion of her Trowbridge ticket at a friends house and had to pay the full single fare on the train.

As we can get hold of the unused ticket what are the refund options, I suspect it will just be on the unused portion of the return iaw the NRCC, and in the
FAQ▸ section of
FGW▸ web concerning refunds.
An expensive lesson learnt if at the end of the day it isn^t worth the hassle.