I am pleased to see this recommendation in The Big Document.
It's not a mask it's a face covering. It's not designed to be impervious to the virus, it's designed to mechanically catch most of your droplets, e.g. coughs, sneezes, tiny flecks of outraged spittle. Think of it as a hanky strapped to your face.
They specifically say that it's a recommendation and that people who would struggle to use a face covering effectively should not do so - e.g. young children, those with breathing difficulties, those with LD, those with sensory issues etc.
Probably some places will go OTT and refuse entry to anyone not wearing one regardless of disabilities or other reasons why it's impractical for certain people and there will then be an outcry and further guidance and staff training will be swiftly provided before they get sued. The same as we have seen with overzealous enforcement of lockdown measures by the police and supermarkets not letting in lone parents who have no choice but to shop with their children.
What I am not so pleased to see in The Big Document is the simultaneous watering down of the 2 metre rule. This is from Annexe A: Staying safe outside your home -
Keep your distance from people outside your household, recognising this will not always be possible. The risk of infection increases the closer you are to another person with the virus and the amount of time you spend in close contact: you are very unlikely to be infected if you walk past another person in the street. Public Health England recommends trying to keep 2m away from people as a precaution. However, this is not a rule and the science is complex. The key thing is to not be too close to people for more than a short amount of time, as much as you can.
Coupled with the main message that those who cannot work from home should be 'actively encouraged' to go back to work, I fear the government's advice on face coverings is less to do with public health and more to do with the economy -
As more people return to work, there will be more movement outside people's immediate household. This increased mobility means the Government is now advising that people should aim to wear a face-covering in enclosed spaces where social distancing is not always possible and they come into contact with others that they do not normally meet, for example on public transport or in some shops
'We know our employees and workers have to travel on rammed buses and tubes if they are to return to work and sadly in our workplace social distancing is just not possible. However we are following government guidance and the government guidance is following The Science. We support our employees to strap a bit of rag to their faces so it's all fine.'