As you’ll be aware, face coverings will become mandatory within shops and supermarkets from Friday 24th July, inline with existing rules for public transport.
You will need to comply with this rule within your store, whether this is through a staff presence at doorways and queue points, extra signage or checks throughout the shop.
You can refuse entry to those who do not adhere (excepting exemptions, such as children under 11, and those with certain disabilities.) The police have formal enforcement powers and can issue a fine – the liability for wearing a face covering lies with the individual.
You can find full Government guidance on how and when face coverings should be worn, and who can be considered exempt at: https://www.gov.uk/government/publications/face-coverings-when-to-wear-one-and-how-to-make-your-own/face-coverings-when-to-wear-one-and-how-to-make-your-own