I was listening to an interview with Peter Horby, who’s chair of the government’s New and Emerging Respiratory Virus Threats Advisory Group (Nervtag). He’s heading up the major Recovery trial into drugs for coronavirus and I suspect knows rather more about virus transmission than anyone on this thread.
He was asked about masks - he doesn’t wear one himself and says the evidence doesn’t warrant making them mandatory or even advisory for people in non-medical settings. Most people don’t wear them properly, they’re not fitted or they wear them walking along the street (where there’s no benefit to anyone either wearer or passerby) and pull them down to talk to somebody else. They’re uncomfortable, hot and have to be changed frequently and the benefits don’t outweigh the negatives. He says that hand-washing, keeping 2m away from other people and coughing or sneezing into your elbow are all more effective at stopping transmission and have less impact on individuals than mask wearing