Face coverings could become a legal requirement in certain settings in England again, if the NHS comes under "unsustainable pressure" this winter.
Health Secretary Sajid Javid said the measure was part of the government's contingency planning.
When could masks become compulsory in England again?
If the NHS struggles to cope this winter, Mr Javid told the Commons face coverings could be mandated again in certain settings in England.
Announcing the government's Covid "Autumn and Winter Plan", the health secretary said face coverings would continue to be recommended in crowded and enclosed spaces and warned they could be legally required once again as part of contingency measures.
Mr Javid said other "Plan B" measures could include asking people to work at home again for a time and bringing in so-called Covid passports.
What is the law on masks across the UK?
- In England, the legal requirement to wear a face covering ended on 19 July
- In Scotland, masks must still be worn in shops and on public transport - as well as pubs and restaurants when not seated. They are required in indoor public spaces in universities and - until at least the October holidays - in secondary schools
- In Wales, masks are still legally required on public transport and in all public indoor areas apart from pubs and restaurants
- In Northern Ireland face coverings are no longer compulsory in places of worship, or for students in school classrooms. They must still be worn on public transport and in shops and hospitality venues
Why are rules different for some transport and shops in England?
Businesses and travel operators can set their own rules for customers and passengers.
For example, Transport for London requires face covering for travel on its services, like the Underground and buses.
In other areas rules differ depending on which transport you are using.
For example, in Greater Manchester, mayor Andy Burnham requires face coverings on trams. He also wants them to be worn on other city transport like buses, but these are privately run.
What if I am exempt?
Most people could be refused service, entry or the right to travel if a firm enforces a requirement to wear a face covering even if it's not legally required.
Companies decide their own health and safety measures, and insisting on masks could be a reasonable rule, says Adam Wagner, a barrister at Doughty Street Chambers.
What have scientists and doctors said?
The British Medical Association, which represents doctors called for the continued use of masks.
England's chief medical officer Chris Whitty and chief scientific adviser Sir Patrick Vallance said they will continue to wear them.
Why use a face covering?
Evidence suggests transmission mainly happens indoors where people are close together.
Face coverings worn over the nose and mouth reduce the spread of coronavirus droplets from coughs, sneezes and while speaking.
The main purpose is to protect others. If everyone wears one, the risks drop for all.
Masks can also help reduce virus spread from contagious people with no symptoms.
Cutting virus transmission is important while many people are not fully vaccinated.
Also, some new virus variants appear more transmissible.
What sort of face covering is best?
- have a nose wire
- have at least two/three layers of material
- fit snugly over mouth, nose and chin
The highest level of protection is provided by FFP3 (or similar) masks worn by healthcare workers in high risk settings. A recent study found FFP3 masks could provid up to 100% protection against Covid.
Hospital staff wearing standard surgical masks were much more likely to catch the virus.
Members of the public can buy FFP3 masks, but they won't provide the highest protection unless fitted correctly.