The UK government has pledged to do 100,000 coronavirus tests a day by the end of April, but was managing about 20,000 with a week to go.
It has now said that up to 10 million key workers and their households in England can ask for a test.
Who can get tested?
Hospital patients, NHS and care staff, emergency services, care home residents and now all essential workers and their families should be able to get tested.
The list of key workers includes teachers, police officers and transport workers.
Testing is not yet available for the general public.
How are the tests being offered?
The tests are done by taking a swab of the nose or throat, which is sent off to a lab to look for signs of the virus’s genetic material. They show whether someone is currently infected with coronavirus.
Key workers in England and Scotland who are self-isolating because they or a family member have coronavirus symptoms can be referred for a test by their employer.
They can also book online themselves and choose whether to attend a regional test site, or ask for a home test kit.
However, with thousands of people using the site since its launch, many have found that tests are no longer available.
If a test is negative, the key worker can return to work if they are well enough, have not had a high temperature for 48 hours, and those living with them test negative.
Wales is adopting a needs-based approach to testing for NHS and “critical” non-NHS workers.
In Northern Ireland,key workers can be tested at one of three drive-through centres.
How easy is it to get tested?
The government hopes to have up to 50 test sites by the end of April. At the moment there are about 30.
But there has been criticism that getting tested is not always simple once a test has been arranged.
The British Medical Association has said the accessibility of centres is a major problem.
And a Dorset residential care home operator said its staff faced a 240-mile round trip to Gatwick for testing.
Why is testing important?
People are tested to diagnose them individually, and to work out how far the virus has spread.
It helps people, including NHS workers, know whether they are safe to be at work.
It can also help the health service plan for extra demand, including in intensive care units.
Testing could also inform decisions around social distancing and lockdowns.
A total of 20,000 households in England will take part in a study to track coronavirus in the general population.
It will help the government identify how much the virus is circulating and whether the rate of infection is increasing.
The findings will help the government’s strategy for easing the lockdown.
How many people a day are tested for coronavirus?
Has the UK been too slow in testing for coronavirus?
There have been suggestions the UK government did not act quickly enough.
The UK did not start with the resources to do mass testing, unlike some other countries.
Countries like Germany and South Korea – which have tested far more widely than the UK – rapidly stockpiled kits and made the test available to a larger number of labs.
As of 19 April, the UK had carried out 6.2 tests per 1,000 people, whereas Germany had done 25.11 per 1,000, Italy 19.93 and South Korea 10.46, according to data collated by online scientific publication Our World in Data from official sources.
Public Health England started with its own eight laboratories, later expanding to a further 40 NHS labs. Then the government said it would involve more laboratories from universities, research institutes and private companies.
UK testing efforts have also been held back by challenges in getting hold of swabs, testing kits and chemical reagents.
However, on 22 April, Dominic Raab, standing in for Prime Minister Boris Johnson, said: “I’ve set the goal of 100,000 tests a day by the end of this month and I’m delighted to say that the expansion of capacity is ahead of plans, even though demand has, thus far, been lower than expected.”
What about antibody tests?
An antibody test shows whether someone has already had the virus.
They work by looking for signs of immunity, by using a drop of blood on a device that works a bit like a pregnancy test.
Mr Hancock has said that 15 of the most promising antibody tests had been tested, but none was good enough.
Tests bought from China identified antibodies in patients who had been seriously ill with coronavirus, but did not pick up the milder cases, according to head of the UK testing regime, Prof John Newton.
The World Health Organization’s head of emerging diseases, Dr Maria Van Kerkhove, said there is no evidence tests can show “that an individual is immune or is protected against reinfection”.
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Correction 25 April 2020: An earlier version of this article incorrectly said that France had conducted just under 140,000 tests a day by 21 April. The figure of just under 140,000 refers instead to the number of tests it had carried out weekly.