Covid: What are lateral flow tests and could they help lift the UK out of lockdown?
Boris Johnson has set out his phased roadmap to ease restrictions as reduced cases and hospitalisations combined with increased vaccinations raised the prospect of getting back to normal.
While coronavirus vaccines are said to be the "cavalry" that will restart the economy, rapid lateral flow tests may offer the security schools and hospitality venues need to open their doors.
Schools are set to return on March 8 and children will now be required to take a test before they can go back into the classroom.
Three million of the rapid-result tests have been sent to employers with staff who can't work from home to identify cases and isolate them quickly. The distribution of free test kits to workplaces will be extended until the end of June.
But lateral flow tests are controversial and divide scientific opinion about how accurate they are. So, what are those concerns and how do they work?
What is lateral flow testing?
These are easy-to-use swab tests that provide a coronavirus test result within 30 minutes, without needing a lab's analysis.
Lateral flow tests are used by the government because they can be carried out at home, providing a fast and simple way to test people who do not have symptoms of Covid-19, but who may still be spreading the virus.
The best-known example of a lateral flow test is the home pregnancy test kit, they detect proteins in a person - in this case, specific to coronavirus.
'One way from now on': Boris Johnson pledges 'irreversible' steps out of Covid lockdown
Seven symptoms should trigger a Covid test, new evidence shows - so what are they?
The test kit is a hand-held device with an absorbent pad at one end and a reading window at the other.
Inside the device is a strip of test paper that changes colour in the presence of Covid-19 proteins (antigens).
The tests are currently being used in mass community testing in areas with high levels of coronavirus, in order to identify symptomless cases, and in care homes to allow visits.
How to take a lateral flow test at home
Taking a lateral flow test usually involves taking a sample from the back of the throat near the tonsils and from the nose, using a swab.
The swab is dipped into an extraction solution. This is then dripped on to the device's paper pad, producing a reaction that gives the result.
The result will be visible on the device precisely 30 minutes after the sample is applied. Unlike a PCR test, there is no need to send the sample to a lab.
How accurate are lateral flow tests?
There have been some concerns that lateral flow tests can provide false negatives - they say someone has not got coronavirus when they actually do.
The government says this is only the case when a test is taken "outside the infectious window", or when the patient's viral load is low and a passing of infection is less likely.
It says lateral flow tests can detect "the vast majority" of cases when levels of virus inside a patient are at their highest and they are most likely to pass on the disease.
How will lateral flow tests be used when children return to school?
In Boris Johnson's roadmap secondary school children will return to school on March 8 subject to twice weekly testing.
The first three tests will be carried out by schools when the children return. If pupils test negative from day one then they can resume face-to-face classes.
Testing at school is to get the youngsters used to performing them before going it alone at home for the foreseeable future.
Mass testing rules also apply to college students. But, crucially, the testing regimen remains voluntary.
Primary school and nursery children will not be required to take a test.
Will a lateral flow test be required to get into pubs and restaurants?
Boris Johnson today said that pubs and restaurants will open from May 17 at the earliest but there was no mention of tests being a condition of entry.
Nightclubs can open from June 21 at the earliest, again with no mass testing regime was set out.
Listen to the ITV News Coronavirus Podcast: