http://forums.moneysavingexpert.com/showthread.php?s=4988b81c6173b25a2ff72f3a9f52098b&t=5389734&page=2#topofpage

...oh I see...so that is how M&S knew...and were then to do that 'show but not tell' exercise with the waterbottles-replaced-by-'coke-it's-the-real-thing'....go figure: