I have gone through a factory reset and reconfiguration with BT and also tried the Personal Hot Spot approach.
My Workstation did Update once, following the Router Reset but has subsequently stopped updating.
The Personal Hotspot fix did not work at all for me.
As I say, in my opinion this is a complex problem and different people will get different results.
I have made BT aware of the fact that many users are likely to experience problems connected with this and they have escalated their investigation of it.
Fortunately, I can do nearly all of my day-to-day work using my iPhone and iPad and my Office 365 is working fine.
So I have no pressing need to update my PC s in the short term.
I feel sorry for those businesses with a large network of PC s who may be dependent on a reliable system being in place for updating them.
The whole point of Windows 10 is to ensure that this is the case but it would seem that there is a significant problem at the moment.
I am sure that it will be sorted out in due course, these things generally are !