Yep, well it should be but no fecker seems to be enforcing it
I think it's so difficult to enforce, even if those charged with enforcing it are full of resolve. But your average Tesco worker, they really won't want the hassle. Given how self entitled many people are these days, as a supermarket worker you can pretty much safely assume that a non-mask wearer is just dying to be challenged so they can get righteous about it.
I was in Morrissons last week and a big argument was going on, a compliant customer had clearly challenged a family of non-mask wearers and dragged a Manager over; The accused father was on such a high horse. Going on about his wife having anxiety, this was her first time out of the house in months, she was moved to tears to be shouted at like this, she may never leave the house again if this is how people are, how dare he, blah blah blah. The wife was stood there looking, well, just bored really. Anxiety my ass. Dad had clearly said "we'll do what we want, no-one will say anything" and I reckon he could try it on another ten times and be right. Most won't challenge.
Not supermarket related I know, but I work for an airline that does enforce it, and enforces it strongly. We tell people right up front that they have to wear a mask to fly, (medical exemptions apply), we tell them at booking, we tell them at check in, we text them, we email them, and finally we address it at the airport departure gate, so when people try it on in flight we won't have it.
Sill I'm up to my neck at the moment with cases where we're banning people, 400 so far, and the excuses just go on and on and on. "They don't work", "I can't breathe", "It's my race you have an issue with", "I have a right not to wear", I've even had one who said "I'm a military veteran, I fought so that people wouldn't be forced to wear a mask". I must admit, I wasn't aware of the war on paper masks.
Unfortunately, people love to try it on these days, and if you want to have a strong policy you need to be ready to fight them all the way. A shelf stacker isn't prepared to have those fights every ten minutes for 8 quid an hour. Who can blame them, it's simply not worth the aggro and the non-wearers know this.