Went to my local superdrug to get some more of my blades of choice today... I usually pay about £3.49 or £3.59 for a pack of 4.
They were on the shelf at £3.59, I think... I picked up a couple of packs and they ran through the checkout at £1.78. Not BOGOF, as the first one ran through at £1.78 before the 2nd one had followed.
Can't see it online, so presume it's just an instore thing... would presume nationwide, but don't know for sure.