The update got stuck on "preparing" at 1%, so I had to reboot. Now it seems to be stuck on "restoring previous version of Windows". At this point I don't know whether Windows is completely trashed. I would have been quite happy if it had only adversely affected some USB devices, instead of this.
Edit: after several hours stuck on "restoring previous version of Windows", I did another reset; Windows finally booted, froze a few times, and is now working OK, minus the update. For whatever reason, the update failed, but Windows was able to automatically recover.
Being a glutton for punishment I am giving the update another go...this time from the support page (
https://support.microsoft.com/en-us/...update-history) rather than Windows update on my PC. Currently it is at 50% downloaded.