Covid 19 Rules and Regulations for Shops

I think I must have missed something somewhere but could any of you please advise me what the current regulations are for wearing a mask in shops?  

I have a couple of queries.  Are the shops supposed not to serve customers without masks and if certain shops are serving customers without masks are they breaching current laws or is there a get out clause for them.  

I had understood that everyone was to wear a mask unless they had a medical condition/exemption preventing them from so doing.  If they have an exemption do they have anything proving this. Do they carry a card for example? 

I had understood that shops were not supposed to serve customers without masks especially when all their staff are wearing them.

Or do the stores have their own guidelines which staff have to follow irrespective of whether or not they are morally right like not being confrontational with customers and still serving them. 

It would be a mockery of the situation if the shops are still allowed to serve the customers without masks.  Does not encourage safe socialisation at all.  If this was the case,  it is putting so many people at risk.  It is particularly insensitive to those who are following the rules and regulations and to those who have loved ones during this horrible time.  

I think that there are a great many cases of "headless chicken syndrome" at the moment in that people think it will not happen to them.  I think we are under a great many restrictions in any event without making situations far more difficult in the long run.

Clarification would be gratefully received before I start firing on all cylinders.

Thanks.

Pattypan