If I understand it correctly shop assistants will be exempted from the requirement to wear masks. This seems illogical. I can understand that wearing one all day would be unpleasant (trust me on this, if you don't then try wearing NBC kit for a while). But if say 1 in 4000 customers may be infected the ones who are and who go shopping may come in to close contact with a few people for comparatively short periods over an hour or two, perhaps just on one day. The 1 in 4000 shop workers who may be infectious will probably come in to similar contact with hundreds of people every day.