Not read the thread but if an employee refuses to work (and he's not claiming he's sick) then you are well within your rights to sack him for breach of contract.
Being "scared of covid" isn't an excuse.
As long as you are putting the proper safe working practices in place then he should work if he is told to.
you're right. its an HR issue really.
you communicate what you expect from your staff
you go from advice from government about what is safe working and show how you are achieving this.
if you cant agree to furlough them because you need them to work then its up to them to turn in for work.
if they dont turn in they need to communicate why they aren't. if they aren't sick its unauthorised leave so you let them know they are absent with unauthorised leave, and then you may give them a another chance, and eventually you sack them or they will most likely just resign.
obviously as far as you are able to, a good employer will try to work out a solution that works for both of you. but if you cant afford to keep them on furlough, and they will not work, they have resigned