No idea about the Tesco in the UK, but in the US what I've seen is that the same places that required you to remove your helmet before, still require you to remove your helmet now, just add - "and put on a mask". I think it's simply that they can't think rationally, just regurgitate the house rules.
In an Indian casino gas station years ago I was heading for the loo and was told I had to remove my helmet, (modular, flipped up at the time). I did so, took care of business and on the way out asked if the security guard had a moment to chat. He was friendly and I kept it friendly too. I showed him how with the chin bar closed like a FF helmet, I could grab the chin bar and wield the helmet like a club very effectively. He asked to hold my helmet and took a couple of mock swings getting a feel for the heft. He took on a very sober expression and looked at me and said "that would hurt for sure". I agreed and told him I just wanted him to have an understanding that when we wore the helmet it might be a "disguise" to him, but the moment we took it off it could become a very effective weapon against him too.
They didn't change their rules, but the next time I went thru there the same guard saw me and motioned me over. He told me that they discussed it at some length at a security meeting and while they decided not to change any policy about wearing or bringing helmets inside, then did amp up some new training on how to defend agains that possibility and had a pretty good discussion on watching for attitude changes when someone was asked to remove their helmet.