A quick question - I purchased an Open ticket for Monday earlier today
from a Thameslink station (Luton Airport Parkway). My plans have no
changed and I won't be travelling.

Does anyone know what refund charge (or admin fee) Thameslink charge
for unused tickets? I'll be passing by Luton on Sunday for my sins,
and it would be nice to know beforehand what there charge is as I
can't find it on their site.

Thanks.