That's turned out to be an interesting one, Avtrician, thank you...
I opened IE for the first time in years and the thumbnails appeared to work as they should (more testing needed!) but the BBC site failed identically to how I described above. I have used Pale Moon for about a year and Firefox for years before that but both of those browsers only began to show these issues since about two months ago when the faults appeared simultaneously (so far as I could tell at the time) for the first time. Your suggested browser change test has brought about the first time when the one fault (BBC News England) has appeared when the other (thumbnails) has been absent which is interesting but still above my pay grade! While I am not going to adopt IE as my browser of choice, the fact that the thumbnails appear to work on it (but not the BBC News England) while failing on the Mozilla-derived browsers may offer a clue to those wiser than I.
Thank you again, Henry Crun, for your suggestion about adblockers. I suspended Adblock Edge and tested the two situations but the problems still occurred. By the way, your posting was passed to me by PPRuNe by e-mail though I didn't see it here on the thread.