At the start of the COVID-19 crisis the official UK government guidance stated that evidence around wearing a face covering suggested it did not protect you or others from any of the coronaviruses.
Later the UK government recommended wearing face coverings in a variety of locations, but did not clarify any face covering standards, and offered mixed messaging in adverts showing masks with valves, dentist masks & even cloth masks.
It is still not clear why there is no guidance on face covering standards, or guidance on swapping cloth face coverings every 2 hours to stop bacterial and fungus growth which can cause chest infections. Source
It is your choice to wear a face covering, some vulnerable groups may wish to take precautions by wearing a face covering.
The government gives specific advice on exemptions on face coverings: More info on face covering exemptions
Can Face Coverings Cause Harm?
Face covering exemptions are available because they could cause the wearer harm, the government has issued exemptions to avoid liability.
Please note, the government advises face coverings, and not masks, these face accessories are not created equal, and some face coverings and masks may be doing more harm than good.
There is a lot of contradictory information on masks, OSEA in the USA have safety, environmental, and risk assessment services, and strict guidelines on mask wearing to prevent injury to the wearer.
Face coverings: when to wear one, exemptions, and how to make your own:
Unmasking mask science
Are Face Masks Effective? The Evidence
Masks: How Effective Are They?
Coronavirus Fact-Check #6: Does wearing a mask do anything?