The government is advising people to take a COVID-19 test before they spend time in "crowded and enclosed spaces" this winter.
The Cabinet Office had previously advised people to take two lateral flow tests a week, especially if they have school-age children or are meeting clinically vulnerable people.
Now the public is being told to take rapid lateral flow tests "if it is expected that there will be a period of high risk that day".
It does not state what a high-risk scenario may be, but it could be an activity such as Christmas shopping in busy high streets or shopping centres.
Watch: The latest COVID cases breakdown from Sky News
The Cabinet Office website says: "You are at higher risk of catching or passing on COVID-19 in crowded and enclosed spaces, where there are more people who might be infectious and where there is limited fresh air.
"You may wish to take a rapid lateral flow test if it is expected that there will be a period of high risk that day. This includes spending time in crowded and enclosed spaces, or before visiting people who are at higher risk of severe illness if they get COVID-19."
On Monday, Prime Minister Boris Johnson said he did not see a need for the government's Plan B to be implemented, but cases remain high in the UK.
Ministers believe the UK is in a better position than countries such as Germany or Austria because of the relatively high take up of the vaccine, and the booster, which has now been rolled out to people aged 40 and over.
Plan B would include mandatory face masks and working from home again where possible.
The government's current advice on face masks states: "You should wear face coverings in crowded and enclosed areas where you come into contact with people you do not usually meet."
It also says one in three people with coronavirus may be asymptomatic but still able to infect others, which is why the lateral flow tests are important.
Rapid lateral flow tests are free and available at pharmacies and online.
Watch: Over-40s can book now their booster vaccine and teens can book their second jab