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.
A further 148 deaths were recorded in the UK on Friday, bringing the total number of recorded deaths to 44,798.
Face coverings have been compulsory in shops in Scotland since Friday.
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, chairman 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 told Radio 4's Today programme: "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."
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It came as Boris Johnson was pictured wearing a face covering for the first time while visiting businesses in his Uxbridge constituency on Friday.
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 on Friday 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."