Everyone in England is being encouraged to have two rapid coronavirus tests a week.
The government wants people to use the tests whether or not they have symptoms.
Why is testing being increased?
The government says regular testing is an essential part of easing restrictions.
It hopes the tests - known as lateral flow tests - can help stop individual cases from becoming outbreaks.
About one in three people have coronavirus without any symptoms.
How do I get a lateral flow test?
If you don't have symptoms, you can get tests from testing sites, pharmacies or through the post (in packs of seven).
If you test at home, you are asked to report your results online or on the phone (by calling 119).
Regular lateral flow testing is already used for frontline NHS, care home and school staff - plus for secondary school pupils and in some workplaces.
How does the lateral flow test work?
It involves swabbing your nose and/or throat, then dipping the swab in a fluid.
This is then dropped onto a plastic device - a bit like a pregnancy test.
A line appears on a paper strip to show the test has worked. A second line appears if you have the virus.
What if I test positive and need a PCR test?
If you get a positive result from a lateral flow test, you and your household must self-isolate immediately.
You should get a PCR (polymerase chain reaction) test to confirm the result.
This can be booked online, or by phone - 119 in England, Wales or Northern Ireland, or 0300 303 2713 in Scotland.
PCR test swabs are sent to a lab for analysis, with the result in 24-48 hours.
How reliable are lateral flow tests?
Lateral flow tests are less sensitive than PCR tests, and can miss more cases, especially in people with mild infections.
However the government says that for every 1,000 lateral flow tests carried out, there was less than one false positive result.
False positives are equally rare for PCR tests.
But they can still cause problems. If lots of people get tested when there is very little virus in circulation, you might get more false positives than true positives, which can distort infection rates.
What if I have Covid symptoms?
You have a legal obligation to self-isolate if:
- You have Covid symptoms - a new continuous cough, high temperature, or change in sense of taste or smell
- You test positive for Covid-19
- You live with someone who has tested positive
- You live with someone who has Covid symptoms (unless they have a negative test)
- You arrive in the UK from a country other than the Republic of Ireland
- You are contacted by NHS Test and Trace to say you have been in close contact with someone who has tested positive