How accurate are the tests?The diagnostic tests used in hospitals are very reliable.
However, that doesn't mean they will pick up every case of coronavirus. A patient at the very start of their infection or with relatively low levels of the virus may show up as a negative.
And a swab may come back negative if it has not picked up enough of the virus from the back of the throat.
So far, antibody tests have not proved to be as reliable.
Health Secretary Matt Hancock said last week that 15 of the most promising antibody tests had been tested, but none was good enough.
https://www.bbc.com/news/health-51943612Why is testing important?There are two main reasons for testing people - to diagnose them individually, and to work out how far the virus has spread.
Having this second piece of information could help the health service plan for extra demand, including on intensive care units.
Testing could also inform decisions around social distancing measures.
For example, if large numbers of people were found to have already been infected, then a lockdown might become less necessary.
And not testing more widely means many people might be self-isolating for no reason, including NHS workers.