I've taken your advice and checked performance over a couple of days. Sure enough, everything has been stable since the downloads completed.
I have to admit to never really paying attention to MS updates over the years, so obviously they've not caused me grief before this. Checking the update history, I see that on the day in question - Dec 19th - there were 120 downloads. During the whole of November there were fewer than 20. My settings allow for updates to be installed automatically (see attached), is that the best option?
Thanks for your help.