Face masks could be compulsory in shops until a vaccine is found – next year at the earliest.
Health Secretary Matt Hancock on Tuesday confirmed they will be mandatory from July 24.
But stretched police chiefs warned imposing the law would be “nigh-on impossible”.
Government insiders suggested the masks would become “part of the new normal” until Britain was through the deadly pandemic.
They warned face coverings could be required until scientists developed a successful vaccine which is unlikely to be available before mid-2021.
Hancock confirmed yesterday that masks would be worn in shops from the end of next week to help control the spread of the virus.
The top Tory claimed that they will give the public “more confidence” to shop as the Government attempts to shore up the battered economy.
The Mirror understands that shoppers could end up wearing masks for months to come – and that they could even be rolled out to other public areas.
One Cabinet source said: “We are not doing this with a timeline in mind. This is part of the new normal.
“Until we get a vaccine we are going to have to be doing a lot of these things.
“We are not going to be doing this for a few weeks and then giving up. It’s part of a wider package of measures, such a social distancing.”
Another Government source added: “I don’t think anybody can know how long it will be but you have to assume we’ll be wearing masks for a while.”
Shadow health secretary Jonathan Ashworth told the Mirror: “Matt Hancock couldn’t tell us how long we’ll need to be wearing face masks but they should be honest with the public and be clear that it’s likely to last for months until we find a vaccine or we are safely through the pandemic.”
Experts warn face coverings should be worn in Britain until coronavirus is eradicated.
Most experts believe eradication is impossible without having a working vaccine, which is not likely to be rolled out until next year at the earliest.
Dr David Strain, lecturer at Exeter University and chair of the British Medical Association’s Medical Academic Staff Committee, said: “We need masks to slow the spread and make life safer for the most vulnerable to go about essential activities.
“Yesterday more than 500 people tested positive for the virus, which the ONS figures suggest is only about a third of the true number of new cases in the UK.
“The remaining two thirds of the population with the virus are the ‘silent spreaders’, people who carry and can potentially spread the virus despite having no symptoms themselves.
“The mandatory use of face coverings will reduce the risk to the population at large from these individuals.”
Incidence rates need to fall to one new case per million per day before masks can be safely removed, he added.
Dr Julian Tang, respiratory scientist at Leicester University, said: “Most of the world’s population is still susceptible to this virus, and we are still not sure how long any post-infection immunity will last.
“So if people can get used to all these precautions now, it will reduce the numbers of Covid-19 deaths over a longer-term.”
It comes after scientists warned that the UK could face as many as 120,000 new coronavirus deaths from the disease without any further lockdowns, treatments or vaccines, with hospitals overwhelmed during winter flu season.
The report, commissioned by Chief Scientific Adviser Sir Patrick Vallance, found that a “reasonable” worst case scenario could see between 24,500 and 251,000 virus-related deaths in hospitals alone, peaking in January and February.
The UK’s daily death toll rose by 138 to 44,968, although the true figure is believed to be higher.
Mr Hancock told MPs that face coverings in shops will give the public “more confidence” to shop as the Government attempts to shore up the battered economy.
He said the policy could be rolled out “in chunks”, and while there were no immediate plans for widening out mandatory use of masks to offices, pubs and restaurants, further measures would be kept under review.
Deaths among shop workers were 75% higher for men and 60% higher for women than among the general public, prompting the need for better protections in retail outlets, he said.
Mr Hancock said the move would be “largely enforced” by the public despite plans for police fines of £100 for shoppers in England who fail to comply.
Stores are being told to refuse entry to people who flout the rules or call the police – triggering a backlash from both retailers and top officers, who warned the move is “impossible” to enforce.
Ken Marsh, chairman of the Metropolitan Police Federation, said: “It will be nigh-on impossible for enforcement because you won’t have a police officer on every shop door because there isn’t enough of us.”
Senior officers were blindsided by the move, with National Police Chiefs’ Council chairman Martin Hewitt saying forces were “unaware” the announcement was coming on Monday night.
Usdaw, the shopworkers union, backed the move towards mandatory face coverings but said staff must not be left to enforce the rules as they were already “dealing with more abuse than normal”.
The decision to make face coverings mandatory in England’s shops, with exemptions for children under 11 and people with certain disabilities, also angered grassroots Tories, with some activists cutting up their membership cards and posting images on social media.
Conservative backbencher Sir Desmond Swayne said it was a “monstrous imposition” that would put him off going to the shops, and warned that his New Forest West constituents were “outraged”.
The shift in stance on masks came after the government’s approach descended into confusion, with ministers contradicting each other.
The move brings the UK in line with 120 countries where masks are required in public spaces, including Scotland, Spain and Germany.
Face coverings have not yet been made mandatory in shops in Wales because coronavirus is at its “lowest ebb” in the country, Wales’ finance minister Rebecca Evans said.
In Wales, masks will only become mandatory for public transport when new rules come into force on July 27.