Is there positive evidence that wearing ordinary masks, not N95 ones, actually makes a useful difference?
Wear masks in crowded public spaces, says science body
Everyone should carry a face covering when they leave home in order to tackle coronavirus, the head of the UK's national academy of science has said.
Prof Sir Venki Ramakrishnan, president of the Royal Society, said the coverings should then be worn "whenever you are in crowded public spaces".
He said evidence shows they protect the wearer and those nearby, and the UK was "way behind" other countries in usage.
No 10 said the use of face masks is always kept "under review".
Current guidance on face coverings varies across the UK, but Public Health England previously said they did not need to be worn outdoors.
Speaking as the Royal Society published two reports on face coverings, Prof Ramakrishnan said the public remained "sceptical" about their benefits because "the message has not been clear enough" and guidelines have been inconsistent.
He added: "What we would like for the government is to be a bit stronger and clearer about the messaging and require it whenever you are in crowded public spaces where you cannot get more than two metres away from the next person.
"If you're in a crowded setting, you ought to wear a mask."