Problems with booking coronavirus tests have eased, after an increase in demand led to local shortages at the start of autumn.
But the laboratory capacity to process tests is lagging behind the government's target of half a million by the end of October.
Should I get tested?
Testing people and then tracing the contacts of those infected is considered vital to stop the disease from spreading.
You should seek a test if you show one of these three key symptoms:
The idea of testing is to find people with the virus and keep them isolated to avoid it being spread through the wider community.
Until you can get a test it's important you and your household self-isolate.
How to get tested
Is the testing system coping with demand?
The testing system experienced plenty of well-publicised problems early on, with people struggling to book.
There were also multiple cases where some people could only book cases many miles from their homes.
But the system is running much better now and coping with demand.
How many tests are being carried out?
Almost 350,000 individual tests were processed on Thursday 22 October. The UK government wants laboratory daily testing capacity to rise to 500,000 a day by 31 October.
It has pledged to bring in mass coronavirus testing by the end of the year, even among people with no symptoms.
The prime minister has spoken of his desire for 10 million Covid-19 tests a day by early 2021, but experts have expressed doubt that this is possible.
What about private testing?
People should only order an NHS test if they are showing coronavirus symptoms, work in certain high-risk settings (such as care homes), or have been asked to have one by the authorities.
Private tests can be obtained from clinics and health centres, with some offering a result within three days.
Prices vary but are often around £100-£200 for a swab test – which shows if you are currently infected – and £50-£100 for an antibody test, which can indicate a past infection. However antibody tests do not work for everyone – and even some people who have had coronavirus do not have antibodies.
Tests must have a ''CE mark'' to show they meet all legal criteria.
If you test positive, the test supplier must let your local health authority know so it can trace outbreaks of the disease and learn more about its prevalence in the UK.
What kind of tests are available?
There are two types of tests.
The first checks if you are currently infected. A nose and throat swab is taken and then sent off to be processed at a lab.
New versions promising to deliver results in 90 minutes are being introduced in hospitals and care homes, where they can be processed using portable machines.
Tests on saliva are also being trialled,.
The second test involves blood samples and looks for antibodies which indicate past, rather than current, infection.
At the moment, these are mainly being used by scientists to estimate what percentage of the population has had Covid, rather than to diagnose individuals.
How reliable are tests?
With the most common type of diagnostic test, scientists at the University of Bristol believe 20% of positive cases could falsely appear as negative – wrongly telling someone they are not infected.
This can be because the swab sample wasn't good enough, there were problems in the lab, or because of the stage of infection the patient was at when tested.
How does the UK compare with other countries?
Each country records testing slightly differently, so like-for-like comparisons won't be 100% accurate.
However, analysis from Our World In Data, a research team based at the University of Oxford, suggests the UK is now performing more tests than many other countries.
For example, on 16 October, the UK carried out 3.9 tests per 1,000 people. This was ahead of European countries including France (3.5), Spain (2.2) and Germany (2).
This just tells us the raw numbers, though, and not how well the tests were targeted.