We have been told by the Government that an effective test, track and trace programme is the key to ‘controlling’ Covid-19, allowing us to further unlock the country and take the economy out of its induced coma. The effectiveness of contact tracing depends on wide ranging factors including how many people have the virus but don’t show symptoms, the accuracy and speed of testing, levels of surveillance, the number of people that come into contact with an infected person and how many people comply with requests to self-isolate.