Success on my desktop!
Decided to try again. Ran Dism /Online /Cleanup-Image /RestoreHealth, no problems reported. Ran sfc /scannow and it repaired some start menu items (which I deleted some time ago as not used):
Accessibility - Windows Speech Recognition
System Tools - Default Programs, Task Manager and Windows Easy Transfer.
I ran the update from downloaded stand alone installer. When it finished and restarted (about 20 minutes for the update and restart) I ran Windows Update and it showed the same update reference with an 11mb file still needed to be installed. Downloaded that
and restarted, and all seems fine. No noticeable change in PC speed, so it seems to have finally done the job.
Did exactly the same thing with the laptop. All went OK.
The only difference, there was not the extra 11mb update this time!
All is well.
Strange that it took quite a few attempts to sort itself out though.