Just come back from Tesco Swindon, and looking at my receipt, it has scanned at the checkout at only 20p. If i had known in the shop i would have got a few more packs!
Not sure if a price glitch, or unknown offer, or if nationwide... but a very good offer i think.
Shelf-full left when i got my pack at midday today. so worth a look-in if your passing.