At risk of telling the world my preferred underwear. Marks & Spencers Bromley at least have a price error on their "3 Pairs Cotton Rich Keyhole Fly Trunks" specifically the pack containing the plum colour (1 solid plum, 2 different black/grey/plum pack). On the receipt the code is 01464894T14, the barcode says M1464894S. They should be £15 per pack buy one get one half price but they scan at £2 a pack! Appears to be that colour set only. The attached picture is a different pack colour but gives you an idea. Good luck!