Most definitely the same book! I made a note in the blog I was keeping on my then website:
Less upsetting [than Childhood's End which I had found depressing] was one of the borrowed books, The Owl Service by Alan Garner which I thoroughly enjoyed. Not simply a brilliant story of ghostly possession, with a real sense of atmosphere and place, but a great evocation of the pettiness and jumbled emotions of adolescence, plus a moral about unintended consequences arising from good intentions. His dialogue is incredible, his sense of character acute. Wonderful.
Since I had wholly forgotten the plot since 2012** (which really is depressing!), I can't swear to any other thoughts I had then, though I can't believe I missed the social comment, but this time around I didn't come away with that same feeling of "Wonderful". I do wonder whether another 12 years of reading fantasy, particularly modern stuff (or just another 12 years of hurtling towards senility...) has corrupted my appreciation of difficult work a little, so now I want more explanation, a little more spoon-feeding of what happens when and why. There was so much dialogue it was almost like reading a screenplay with some stage directions, and I definitely didn't get the same sense of atmosphere and place this time, and rather ached for poetic nature-writing of the kind you do so well.
It might just be, though, a matter of mood and situation when I was reading it. I'll perhaps leave it another 6-8 months and give it a re-read.
** oddly enough, although I couldn't remember anything about the characters and storyline, I did immediately recall the image of the plate at the beginning, probably because I'd stared at it so much trying to see where the owls were!