The government will announce whether masks should be made mandatory in English shops later this week, Boris Johnson has said.
The prime minister, who has been criticised for "confusing" public health messaging on the issue, said a decision would be made on regulations in "the next few days".
Public health experts and retail chiefs have been urging the government to look again at making face masks to encourage people back to the high street and stop the spread of coronavirus.
"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 told broadcasters on Monday.
"We will be looking in the next few days about exactly how, with what tools of enforcement, we think we want to make progress.
"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."
But Mr Johnson's deputy, cabinet office minister Michael Gove insisted yesterday that masks would not become "mandatory" but suggested it was "basic good manners" to wear one.
As recently as April Health Secretary Matt Hancock was actively discouraging the wearing of masks, suggesting that they were ineffective and that public uptake of the practice would create shortages for NHS workers.
"When the pandemic was declared by the WHO 70 countries already required their citizens to wear masks in enclosed places or strongly recommended it - now it's 120," Linda Bauld, professor of public health at the University of Edinburgh told the BBC on Monday morning.
"Part of the reason for that is that the science has moved on in that there are new studies, and new reviews. The second thing is that the WHO themselves commissioned research to look at it, essentially bringing together all the studies, and they changed their advice."
Mask-wearing was made mandatory in Scotland last week but there are still no clear rules in England. Professor Bauld said that "three or four months ago" some of her colleagues in the UK were unsure of the evidenced supporting face coverings, but that "now some of those that were quite uncertain some time ago are now definitely saying that new evidence suggests that we should be wearing these".
James Daunt, the former Waterstones boss who now runs bookshop chain Barnes and Noble, said a "firm direction" from the government would encourage people to take up masks and could help build confidence.
On whether requiring their wearing would give people the confidence to return to shops, Mr Daunt said: "I don't think it's a huge factor, but I also think if it reassures people it's a perfectly sensible measure to take."
He said mask wearing would "become normalised" with time but warned that retail workers should not be asked to "police" any enforcement.
"I think it's certainly about changing attitudes but clearly if there is a firm direction that masks should be worn then the vast, vast majority of people will," he said.
"But I definitely do not think shop workers should be the police of it – that would not be right. Because there are a tiny, tiny minority of people who will be confrontational over it and it is not the position of shop workers to enter into that situation.
"We would indeed not ask out shop workers to confront someone who was stealing from us - we would ask them to call the police.
"So we shouldn't put ourselves in confrontational positions, but I think we can as retailers, if we are requested to do so, clearly tell everyone it's a sensible thing to do."
The prime minister himself appeared on Friday wearing a mask for the first time. But some influential right-wingers close to the governing Conservative party have complained about proposed mandatory mask-wearing and other lockdown measures, including in the government-supporting Daily Telegraph newspaper which the prime minister has regularly written for.
Cabinet office minister Mr Gove suggested on Sunday that the government was unlikely to take regulatory action, adding: "I don't think mandatory, no, but I would encourage people to wear face masks when they are inside, in an environment where they might be mixing with others and where the ventilation might not be as good as it might. I think it is basic good manners, courtesy, consideration, to wear a face mask."
But speaking to the BBC on Monday morning Professor Bauld said: "In a retail environment what we'd want to see is customers wearing them, or even the visors, or having the perspex screens – so thinking about the whole setting, not simply masks or not.
"From a behavioural science perspective I think it's jolly confusing the messaging we've seen in the last few days ... it's much better to be clear and consistent and we need to do a few things: you need to lead by example. So leaders need to wear them, that's been highly variable across the world. You need to explain to the public why it's being recommended or required.
"And I think the thing about requiring it is it basically just says to people that this is expected, and even if enforcement is not heavy handed, and I don't think it needs to be in this case, the fact that it's required makes a difference. Just observing locally here (Scotland) I'd say about 1 in 5 people were wearing them in my local supermarket, but when I went there yesterday only one person wasn't wearing one, and they may have had a reason. Requiring them just gives that little extra nudge."