Video report by ITV News Political Correspondent Dan Hewitt
An announcement on whether face coverings should be mandatory in shops in England is expected "in the next few days" following mixed messages on the issue from the government.
During a visit to the London Ambulance Service, the Prime Minister told reporters: "Yes, face coverings, I think people should be wearing in shops, and in terms of how we do that – whether we will be making that mandatory or not – we will be looking at the guidance, we will be saying a little bit more in the next few days."
Mr Johnson added: “We will be looking in the next few days about exactly how, with what tools of enforcement, we think we want to make progress (over coronavirus)."
'I think people should be wearing them in shops' says Boris Johnson:
“As the virus comes down in incidence and we have more and more success, I think face coverings are a kind of extra insurance we can all use to stop it coming back and stop it getting out of control again.
“To be absolutely clear I do think that face coverings do have a real value in confined spaces and I do think the public understand that.”
The government's position on the issue has appeared up in the air over the past few days, after Boris Johnson hinted that stricter rules could be brought in for the wearing of "face coverings in confined spaces".
Over the weekend, Michael Gove was forced to clarify Number 10's position suggesting the public should be "encouraged" to wear face coverings.
Meanwhile, Justice Secretary Robert Buckland added another option into the mix on Monday.
Mr Buckland told ITV News it was "common courtesy" to wear a mask in "an enclosed space, like a shop".
He added, however, that the government "trusts people to do the right thing" and so will not be making the rule mandatory.
Quizzed on BBC Radio 4's Today programme whether he was in the "mandatory perhaps" or "mandatory never" camp, Mr Buckland said: "I think I’m 'mandatory perhaps'."
Quizzed on the conflicting responses at the top of government, Mr Buckland said: "He (Mr Gove) took the view as he was answering the question that he thought we should encourage good sense - I agree with that."
But added: "If it becomes necessary to nudge people further by taking further action then of course we will consider that.
"I think the matter is under careful and daily review."
The Justice Secretary told BBC Breakfast: "A small shop I think is a very sensible place to wear a covering".
He added: "I think a mask is just an additional helpful mitigation that isn't just an act of courtesy. I think it's an act of increasing safety and public confidence."
The use of a mask alone is not sufficient to provide an adequate level of protection, according to WHO advice. Other measures such as physical distancing and hand hygiene should be adopted.
The call for ministers to make face coverings mandatory in shops in England has been growing following First Minister Nicola Sturgeon's decision to change the rule in Scotland.
Downing Street has also faced questions about why more Cabinet ministers are not wearing face coverings.
A photo opportunity for the Chancellor's new "eat out to help out" scheme saw Rishi Sunak serving food to customers in one restaurant while not wearing a face covering.
Labour has demanded "clarity" on the government's position and has requested that Health Secretary Matt Hancock come to the Commons on Monday to provide Parliament with a "clear message".
Shadow health minister Justin Madders told BBC Radio 4's Westminster Hour: "We need Matt Hancock to come to the House and say this is what the science says, this is what we believe you should be doing and then let's move on."
Dr Venki Ramakrishnan, president of the Royal Society, told ITV's Good Morning Britain that the evidence on face coverings had "shifted".
The Scientific Advisory Group for Emergencies (Sage) member said: "It’s (evidence) now quite strongly in favour of using face coverings in enclosed spaces where we're likely to come into contact with strangers.
"I think that the government should be very clear. It's not consistent to make it mandatory on public transport and not make it mandatory in other enclosed and busy public spaces because the behaviour of the virus is the same in all of these spaces."
James Daunt, managing director of Waterstones book stores, said asking customers to wear a face covering was a "reasonable measure".
When asked if the policy could boost shopper confidence, he told the Today programme: "I don’t think it is a huge factor, but I also think if it reassures people, then it is a perfectly reasonable measure to take."
But he said staff working across his chain of stores would not be asked to "police" the wearing of coverings.