i took mine to threshers and had a chat with the manager about it
the whole thing about it not being intended for public release is just a chinese whisper..
basically its a good deal, but not as good as it sounds.. nearly all wine in threshers is buy 2 get 1 free. and you cant use it in conjunction with that offer.
you can still buy all those wines but at the full price, and then 40% off..
eg:
you want to buy 3 bottles of wine for a fiver each
normally it would be 5 + 5 + 0 = 10
with the voucher its 15 quid with 40 % off = 9 quid
so realistically the voucher is 10% off and not 40% (in the above situation)
however, if you only want one bottle then you get 40% off instead of 0
here endeth the lesson
PS its only valid on wine and champagne
i think its also valid in some other shops such as majestic wine warehouse, but i might be wrong.. might even get a better bargain in there