Face coverings have a “weak but positive effect” in reducing the spread of coronavirus, Downing Street has concluded, but ministers are still deciding the details of the advice to issue.

Boris Johnson suggested that coverings will play a part in his announcement on how the lockdown measures may be eased, which the PA news agency understands will not come before next Thursday’s review.

The Government had been resisting calls to recommend their use despite Scotland’s First Minister Nicola Sturgeon advising the public to use cloth face coverings when in enclosed public spaces.

The Prime Minister’s official spokesman acknowledged on Friday that the evidence shows they can reduce the spread of the virus from infected individuals who are not showing symptoms.

“The advice we have received based on the science shows a weak but positive effect in reducing transmission of coronavirus from asymptomatic members of the public where social distancing isn’t possible,” he told journalists.

“What ministers need to consider is how best to produce advice for the public on the next steps, and that work is still ongoing.”

Mr Johnson told his first Downing Street press conference since being admitted to hospital with Covid-19 that coverings “will be useful” to both slow the spread of the disease and give people “confidence” to go back to work, after fears there may be hesitance after weeks of firm messaging to stay at home.

Experts do not believe that rudimentary coverings give much, if any, protection to the individual wearing them.

Ministers are understood not to be considering recommending the use of medical-quality masks, advice which may divert supplies away from the front line.

One issue they are considering is what kind of materials to advise to be used as coverings.

The PM promised to deliver a “road map, a menu of options” next week on how he would get the economy moving again and get children back to school while still suppressing the disease’s spread.

That plan is not expected before Thursday, which is the latest date ministers must review the emergency measures under legislation.

The PM is likely to first hold a discussion with his Cabinet and hear more from the Scientific Advisory Group for Emergencies (Sage).

The updated guidance on masks is also expected next week, though No 10 acknowledges the subject is not simple.

The PM’s spokesman said Cabinet Office Minister Michael Gove was “accurately reflecting the position of the science” when he warned that face coverings could encourage people to act in a more “cavalier” manner.

Housing Secretary Robert Jenrick said wearing coverings will be a “personal choice” because they only make a “modest difference” in the fight against Covid-19.

“It’s a personal choice, if you have a face mask, it’s your choice whether you want to use them, and if you walk around some of our towns and cities today you are seeing more people using them than ever before,” he told the BBC.

“The advice today is that the difference made by a face covering is quite modest – it doesn’t make a huge difference but it does make some. So it’s your choice.”

London Mayor Sadiq Khan, who has long been calling for wider use of masks, welcomed the PM’s movement on the subject of coverings, saying they would play an “important role” in lifting lockdown restrictions.