Think it would have a much greater effect on reducing transmission if masks were worn inside all the time.
Is there evidence that the virus is spreading in the open air with people keeping their distance? Most transmission is indoors.
Of course mandatory mask wearing in public outdoors would be much easier to enforce (mainly by public peer pressure, not policing per se) - which is why it's not seen as a stupid question - but along a path in rural Lantau? Mandating indoor mask-wearing would be nugatory - in any country in the world, let alone a liberal democracy. Routine in health care and care settings though, and rightly so, given the threat and the necessary constant mixing of individuals.
How do you think a yahoo poll asking this would go?
"Have your say: Should everyone wear face masks indoors in the UK?"
