Just picked up a can of raspberry kombucha with my meal deal at a train station M&S, and had to wait for a store attendant to come and authorise my purchase to say I was over 16. I asked her why and she said "because it's fermented" which cannot possibly be correct, so is yoghurt FFS.
Anyway I wasn't about to argue with her because she won't be in charge of the policy but wtf? It can't be because of concerns over alcohol content because that would be 18+ not 16+. Caffeine? But it's probably got less in than coca cola and they don't restrict that 