MPs have called for the government to clarify its position on face coverings, after the PM said a "stricter" approach to their use in England was needed. Senior sources have said the government is considering making face coverings mandatory in shops in England to slow the spread of coronavirus.
Former Health Secretary Jeremy Hunt said he was "in favour" of the change, adding a simple public message was key.
Labour MP Jonathan Ashworth said "strong and clear guidance" was needed.
When a further 148 deaths were recently recorded in the UK, it brought the total number of recorded deaths to 44,798.
Face coverings have, in recent days, been compulsory in shops in Scotland, while currently people in England are advised to wear a face covering in enclosed public spaces where social distancing is not possible - on top of the mandatory requirement to wear one on public transport and when visiting hospitals.
Mr Hunt, chair of the Commons Health Select Committee, said he understood the current advice but it did not answer the "basic question" of whether people needed to wear a face covering when shopping. He said: "I think with public health advice in a pandemic, you just need simplicity so I would favour saying we should wear face masks in shops."
It came as Boris Johnson was pictured wearing a face covering for the first time while visiting businesses in his Uxbridge constituency.
The UK government was initially hesitant - in the early days of the coronavirus crisis - about advising people to wear face coverings, arguing the scientific evidence that they reduce transmission was "weak".
However, rules compelling people to wear face masks on public transport in England were introduced on 15 June.
And Mr Johnson said "the balance of scientific opinion seems to have shifted more in favour of them than it was, and we're very keen to follow that".
He told a Facebook Q&A with the public: "I do think we need to be stricter in insisting people wear face coverings in confined spaces where they are meeting people they don't normally meet.
"We are looking at ways of making sure that people really do have face coverings in shops, for instance, where there is a risk of transmission."
Wales' First Minister Mark Drakeford said he did not think the evidence on the benefits of wearing facemasks was "decisive" yet but said the "balance is shifting".
He said the view of the chief medical officer for Wales was still that face coverings should be recommended but not required. However, he said if the weight of evidence changed "then we will change our policy".
The rules on face coverings vary across the nations. People in Wales are being asked to wear non-medical face coverings where social distancing is not possible. In Northern Ireland, wearing face coverings on public transport became mandatory on 10 July.
Shadow health secretary Ashworth said it was "welcome" ministers were looking again at the evidence on face masks.
"We urge ministers to conclude this review rapidly to provide the strong and clear guidance needed," he wrote on Twitter.