The main public health technique for controlling epidemics returns to England tomorrow with the start of the NHS Test and Trace service. ..... Anyone with corona virus symptoms will be asked to self-idolate and book a test. If the test delivers a negative result, the self-isolation ceases but if it is positive the service will contact them and try to work out all their contacts - people who have been within 2 metres of them for more than 15 minutes in the last few days. These contacts will be asked to self-isolate for 14 days or 7 days after they develop symptoms, whichever is shorter.