Found 4th Feb 2017
I'm not sure if this was just a one-off glitch, but I thought it was worth sharing just in case as my other half got a great deal at the Superdrug in Woolwich, London. It was marked on the shelf as £4.98 just like the price shown on the website, but scanned through as just £1! I'll upload a picture of a receipt showing this. It might be worth a check.