Re: The crucial number ...
From today's Financial Times* (front page article - their website has a paywall):
"Yet less than 65 per cent of total laboratory testing capacity had been used in November and December. Even with this spare capacity, test and trace had never met the prime minister's commitment to turn around all tests in face-to-face settings in 24 hours - a goal he had said would be met by the end of June."
*(I only get it when there is an article I want to read, it is a bit too pricey for every day at £2.90, and the web site subscription is £35 per month!)