Found this new offer on the priority moments app though doesn't seem to be available online.

£5 off your shop at HMV, no minimum spend mentioned in the T&Cs! There are restrictions on what it can be used against; no tablets, gift vouchers, tickets, etop ups, warranties and the usual cannot be used in conjunction with any other offer but no mention of a minimum spend.

http://www.o2priority.co.uk/moments