First things first, deciding to only test serious cases is either a political or economic choice and not a scientific one. Evidenced by the fact that those with means are privately tested whenever they like.
The UK stuck it's neck out and then subsequently got in line, in the process wasting a load of time. By doing this, the people involved opened themselves up to scrutiny, especially after we dramatically changed course to fall back into line with the rest of the world over last weekend.