Instructions:Got this in an email earlier, as the T&Cs say "existing customers only" I assume it's not account-specific! (The jpeg says "first shop" - not sure why, been with them for years!).
Might be worth trying if you're new, not sure if that's a mistake!
Code THXMAS expires 16th December 2016 @ 23:59. Valid for existing customers only. Cannot be used in conjunction with any other offer.