So, since making my 'Ubiquity' post over the weekend, I've now heard, both through the comment to the post and in private e-mail (thanks 'Trotter'; thanks Mike) that 'Giles' is a traditional farmer-name in England, rather like 'Jeeves' has become a joking default butler name over here (ironically so, since Wodehouse's Jeeves is not a butler but a valet). The piece in BBC HISTORY MAGAZINE obviously drew on this traditional lore, then, not JRRT's little story. But I suspect the reference in FOYLE'S WAR (see my post of Jan. 25th) genuinely does refer to Tolkien, since it mentions the blunderbuss as well.
Unless, of course, both 'farmer Giles' AND his blunderbuss are part of the traditional lore, in which case FGH is closer to, say, Tolkien's recasting of 'Cat & the Fiddle' than, say, THE HOBBIT. If anyone knows more about how far back 'Giles' goes as the generic farmer name, or any pre-Tolkien connection of that stock name with a blunderbuss, I'd be v. interested to hear about it.