Having just treated myself to a new PC (see below), I downloaded and attempted to install the SH 4 1.4 patch: blowed if I didn't encounter that same confounded "Administrator Blocked" nonsense. (Typical Windows, making life harder for ordinary users by adding extra garbage)
I went through the steps outlined on
this page : using the "Run the app/file via Hidden Administrator Account", I was able to install the file and, having installed SH 4 from the disc, right now there are no problems starting/running the game through the shortcut on my desktop.
Still, to make doubly sure that Microsoft don't screw up the game in future, I'm going to uninstall and reinstall SH 4 & patch 1.4 into a discrete folder on a different partition.