Britons should be wearing masks in shops, with face coverings offering a "great deal of value" in controlling the spread of coronavirus, Boris Johnson has said.
The government has been criticised for offering mixed messages on face coverings, with it mandatory to wear one on public transport in England but not in shops.
But the prime minister on Monday signalled the guidance could change this week after he admitted there had been "growing" evidence of their importance during the COVID-19 pandemic.
He said: "What we've said for a while now is that we do think masks have a great deal of value – obviously they're mandatory on public transport, on the Tube – but they have a great deal of value in confined spaces, where you're coming into contact with people you don't normally meet.
"What's been interesting on the face coverings issue in the last few months is the scientific evaluation of face coverings and their importance in stopping aerosol droplets, that's been growing.
"So, I do think that in shops it is very important to wear a face covering, if you're going to be in a confined space and you want to protect other people and to receive protection in turn.
"Yes, face coverings, I think, people should be wearing in shops.
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"And, in terms of how we do that, whether we make it mandatory or not, we will be looking at the guidance, we'll be saying a little bit more in the next few days."
Mr Johnson added that the government would be looking at "what tools of enforcement" might be introduced to "make progress" on the wearing of face masks.
He described the wearing of a face covering as an "extra insurance that we can all use to stop it [coronavirus] coming back and stop it getting out of control again".
Currently, official UK government guidance states that evidence around wearing a face covering suggests it "does not protect you" from coronavirus.
But the guidance adds: "If you are infected but have not yet developed symptoms, it may provide some protection for others you come into close contact with."
In England, Scotland and Northern Ireland, face coverings are mandatory when travelling on public transport.
Face coverings are also mandatory in Scottish shops, although that is not the case in England.
People in Wales will have to wear a face covering on public transport – as well as taxis – from 27 July, First Minister Mark Drakeford announced on Monday.