Clients crashed last w/e
Wish I'd seen this before now, as tried all tricks to recover system, but had to bite the bullit and do a re-install - fortunately all personal data was on a separate drive.
Of course system was using Avast, will now expect to see others.
The whole concept of Microsoft updates on Win10 is ill-thought out and is, in my opinion, the reason why more users are either moving away to alternatives - some have also gone back to Win 7. Microsoft need to go back to the drawing board on the update process.
I'm sticking to Win 7 on my personal multiboot system (rarely use win 10)