Working safely during COVID-19 in offices and contact centres, published 24 June 2020, states:
6. Personal Protective Equipment (PPE) and face coverings
(Emphasis mine)
Unless you are in a situation where the risk of COVID-19 transmission is very high, your risk assessment should reflect the fact that the role of PPE in providing additional protection is extremely limited.
6.1 Face coverings
There are some circumstances when wearing a face covering may
be marginally beneficial as a precautionary measure. The evidence
suggests that wearing a face covering does not protect you, but it
may protect others if you are infected but have not developed
symptoms.
It is important to know that the evidence of the benefit of using a face covering to protect others is weak and the effect is likely to be small…
Advice for offices and contact centres: https://assets.publishing.service.gov.uk/media/5eb97e7686650c278d4496ea/working-safely-during-covid-19-offices-contact-centres-240620.pdf
Advice for restaurants, pubs, bars and takeaway services: https://assets.publishing.service.gov.uk/media/5eb96e8e86650c278b077616/Keeping-workers-and-customers-safe-during-covid-19-restaurants-pubs-bars-takeaways-230620.pdf
Advice for close contact services: https://assets.publishing.service.gov.uk/media/5ef2889986650c12970e9b57/Keeping-workers-and-clients-safe-during-covid-19-close-contact-services-230620.pdf