Coronavirus testing: What is a false positive?

There has been a lot of talk on social media about "false positive" test results after several commentators suggested they might be seriously skewing the coronavirus figures - but that is based on a misunderstanding of the impact of false positives. Talk Radio host Julia Hartley-Brewer has claimed that "nine out of 10 of the positive cases of Covid we are finding in the community when we do random testing, when anyone just puts themselves forward, will be wrong. They will not be people who have got coronavirus." Could it be true that 90% of positive results from tests in the community - that means tests not carried out in hospitals - are false? The answer is "no" - there is no way that so-called false positives have had such an impact on the figures.