I had to pop into Sainsburys and Marks today and hardly anyone had a mask on. I am vulnerable, so still wear one, and felt a bit conspicuous! I do think age of customers ( and therefore vulnerability) is the main difference between stores. My nearest Asda ( next town) is near university and college ( lots of young adults shopping) and near large housing estates (adults shopping for families) Sainsburys and Marks and Spencer’s on the other hand are at an out of town sight ( together) and attracts mostly people who shop by car, as well as from our village, so may have a wider range of customer demographics.
On trains ( commuter) despite the crowding, rather less than half wear masks. Men ( young and middling) and younger women mostly don’t. Older commuters like myself usually do.
Mask wearing in English shops are no longer mandatory, but still advised.