Covid can be spread through a number of routes, including virus-containing droplets emitted when an infected person breaths, speaks or coughs – a factor experts said could help to explain why Covid seems to spread more easily in indoor settings.

The team concluded it was unsafe to stand without a mask two metres away from an infected person who is talking or coughing, with both situations posing an infection risk.

The team add that an hour after an infected person has spoken for 30 seconds the total aerosol left contains much more viral mass than after one cough – adding that in small spaces and without ventilation this might be enough to cause Covid.

The team have used their work to develop an online calculator, called Airborne.cam, for users to explore their risk of becoming infected indoors via airborne particles alone.

While the infection risks are only theoretical estimates, and are not specific to the new UK coronavirus variant, the team said the tool can help users to explore ways to stay safe in different scenarios.