Well, following some advice on the
Winhelp site, which said that these scans can take
up to 8hrs on a machine that has never been updated, I left mine on overnight (with all the power-saving options turned off - so it could not automatically shut down) and, lo and behold, this morning there were 167+ important, and 60+ optional, updates available to download!
Now doing that, and will then create a bootable flash drive image of the updated config (need to get a 64GB drive for that) before I attempt the Win 10 upgrade again - then I will decide if I will get back to the W7 config level.
PS: lucky that I have unlimited fast cable broadband for the downloads as there are 900MB of them - I think it will take about an hour or so (getting slower!).