Every Thursday evening between March and July, the British public faithfully turned out on their doorsteps to clap for the National Health Service “heroes” on the coronavirus frontline. Rainbow signs that read “Thank You NHS” still festoon the country. Almost 650 health workers have died from Covid-19, a death toll topped only by the US and Mexico, according to Amnesty International.Now the NHS faces more strain heading into winter because of a shortage of Covid-19 tests – a system Prime…