Testing, the government keeps telling us, is the way out of the coronavirus lockdown. Soon, the Prime Minister assured us in his address to the nation last Sunday, we will be testing ‘literally hundreds of thousands of people every day’. Given that Matt Hancock seems finally to have achieved his ambition of testing 100,000 people day – as he promised to achieve by the end of April – who could doubt that the PM will realise his promise?

True, there was some controversy over the way that the health secretary reached his 100,000 tests on the very last day of April,...