From Friday 24 July, it will be mandatory for people to wear a face covering whilst in retail outlets (e.g. indoor dealerships/sales offices) in England. Face coverings in shops are already mandatory in Scotland.
It is suggested retailers display signage at the entrance to the store to remind visitors of this policy and consider having a supply of masks for customers. However, staff are not expected to police this, but should explain, if challenged, why you have adopted this policy, i.e. to keep others safe and limit the transmission of Covid-19.
You can ask customers to temporarily remove their face coverings in the event that you have to identify someone against e.g. their driving licence or other ID.
Government guidance on exemptions, face covering at work and how to dispose of coverings can be found here.