The Tories finally published a full list of places where face masks must be worn just hours before the law come into effect tomorrow.
People will have to wear one over their nose and mouth in all shops and supermarkets in England.
Post offices, banks, railway stations and airports are also on the list.
It will also be mandatory to wear a face covering when buying takeaway food and drink.
Labour and retailers say the Tories have been mired in “confusion”.
After months claiming masks were unnecessary or would give false confidence, No10 changed the rules as part of new restrictions in a bid to prevent a potentially catastrophic second wave of Covid-19 this winter.
The UK’s official death toll rose today by 53 to 45,554, although the true figure is much higher.
Ministers said face coverings are now part of the “new normal” and the public will be told to wear them for the foreseeable future.
Stores can refuse entry to those without a mask or who fail to wear one properly. Police can use “reasonable force” to remove the shoppers and may impose £100 fines.
But officers say the regulations, which will be in place for a year, will be almost impossible to enforce.
Venues such as eat-in restaurants, pubs, hairdressers, beauty salons, gyms, leisure centres, cinemas and theatres will all be exempt – as long as they have other protection measures in place.
It is already compulsory to wear face coverings on public transport.
They can be fabric, such as a scarf, but research suggests home-made coverings need to be at least two layers thick, preferably three.
The disabled and under-11s are among those exempt from the new rules. People can briefly remove their mask if, for example, staff ask for ID.
Public Health England has warned parents not to use face coverings on babies and young children due to the risk of choking and suffocation.
Ministers have been urged to do more to protect those exempt from wearing masks after a charity highlighted “horrific” cases of disabled people being abused.
The public are advised to wash their hands before putting a covering on or off, and to avoid touching their face while wearing one.
Health Secretary Matt Hancock said: “As we move into the next stage of easing restrictions, it is vital we continue to shop safely so we can make the most of our fantastic retail industry… Everyone must play their part in fighting this virus by following this new guidance.”
But Shadow Health Secretary Jon Ashworth told the Mirror: “After weeks of ministerial muddle and Cabinet confusion finally face masks will be mandatory in shops.
“Why it took so long to get to this point is yet another example of this Government’s slow response to the pandemic.” The Tory announcement came after last-minute confusion over how and where the rules applied.
Some ministers seen in takeaways recently wore masks and some did not.
The rules clarify that in places such as McDonald’s, you do not need a mask if you are sitting down to eat. But you do if you are taking food or drink away.
Major retailers and unions said they would not ask staff to enforce the rules in case it puts them in harm’s way.
Paddy Lillis, of shopworkers’ union Usdaw, said: “They are already dealing with more abuse than normal and this could be another flashpoint.”
Some employers said they would not require their staff to wear coverings if they work behind plastic screens. Tom Ironside, of the British Retail Consortium, said: “Retailers are doing all they can to support necessary safety regulations and will play their role in communicating and encouraging the Government’s policy on face coverings.
“While enforcement of this policy will be handled by the police, the ultimate responsibility remains with customers.”
Ministers have been accused of mixed messaging on the issue.
Kate Nicholls, chief executive of UK Hospitality, said the latest regulations contradicted what the industry had previously been told and it was “very late in the day” for confirmation.
She added: “It’s really unhelpful to have that confusion because the single biggest thing we need now is to rebuild consumer confidence and that needs clear, unambiguous messaging.” Britain’s most senior police officer said she hoped any shoppers refusing to wear masks will be “shamed” into complying.
Metropolitan Police commissioner Dame Cressida Dick added if staff were worried and had attempted to handle the issue then officers would try to help. She said: “Calling the police should be a last resort for dealing with a mask issue.”
As ministers prepares for a possible surge in Covid-19 cases this winter, people living in cities or large towns should be within a 30-minute walk of a testing site by the end of October.
And hundreds of walk-in testing centres are due to be set up.
NHS Test and Trace is recruiting more people as the system prepares for any rise in cases in the colder months.
It comes as Tony Blair warned that coronavirus will not be eliminated and that Brits must learn to live with it.
The former Prime Minister also urged ministers to focus on containment measures in the months ahead.