The rest was tough but doable. I guess my clue of the day is 9ac, for its nice structure and echo of the wonderful TV series. Thanks to the setter.
Clues are in blue, with definitions underlined. Answers are in BOLD CAPS, then wordplay. (ABC*) means ‘anagram of ABC’, with the anagram indicator in bold italics. Deletions are in [square brackets].
Across
1 It’s Let It Be that concludes this great live event (4)
STET: last letters (“this concludes”) of the last four words.
4 Fish surprises, served with chopped fruit (4,6)
ROCK SALMON: ROCKS / ALMON[d].
9 Rumpole pays out, scrapping over sweetener (5,5)
MAPLE SYRUP: (RUMP-LE PAYS*), having “scrapped” O for “over”.
10 Irish drawn to saint excited reaction (4)
STIR: ST (saint) / IR (Irish).
11 Mountain girl in historic subcontinental region (6)
BENGAL: BEN / GAL.
12 Always travelling west, minister in eastern capital (8)
EVERMORE: REV inside E / ROME, all reversed (“travelling west”).
14 Pass through having taken in Slovakia’s capital (4)
VISA: S[lovakia] taken in by VIA (through).
15 Support British on search for swimmer (10)
RIBBONFISH: RIB / B / ON / FISH (search).
17 Cook has minutes to find relish (10)
ENTHUSIASM: (HAS MINUTES*).
20 Mock Shakespeare’s ending in Tempest (4)
RAGE: RAG (mock) / [shakespear]E.
21 Letters Heather’s about to bring in (8)
LEARNING: LING “about” EARN.
23 Old Greek sailor turning in as consequence (6)
THEBAN: AB “turning” in THEN (as consequence).
24 Good to deliver in box (4)
GRID: G / RID. Chambers gives “grid” as “framework”, which seems near enough.
25 Party girl Formula One founder entertains (6,4)
FIANNA FAÍL: ANNA (not ANNE, obviously, if you know the answer you’re looking for, although in that case you hardly need the wordplay!) “entertained by” F1 / FAIL (founder, as in “sink”). It’s an Irish political party.
26 Mimicking bird, cat who looks for excitement? (7,3)
PEEPING TOM: PEEPING (mimicking a bird) / TOM (cat).
27 Connection used by school in Karachi (4)
LINK: hidden answer.
Down
2 One to elicit pity generated in plays? (11)
TRAGEDIENNE: (GENERATED IN*).
3 Communications device to signal unwittingly (9)
TELEGRAPH: double definition, the second as in “he telegraphed his next move”.
4 Sovereign holds good man to be lawbreaker (7)
RUSTLER: RULER “holds” ST (saint).
5 Figure Caribbean agents may give (5,5,5)
CERNE ABBAS GIANT: (CARIBBEAN AGENTS*). The exact spelling is a punt unless you know the answer. It’s a hillside figure in Dorset.
6 Drink on tick for boss (7)
SUPREMO: SUP / REMO (another name for Riesling, apparently). I didn’t know this name for the grape, but this time the answer was obvious. On edit: forget that nonsense! A sensible parsing suggested in the comments is SUP (drink) / RE (on) / MO (tick).
7 Noise from the herd about race becomes slogan (5)
MOTTO: MOO (noise from the herd) “about” TT (motor cycle race).
8 Message sensibly delivered in this bottle? (5)
NERVE: double definition. The first alludes to signals to or from the brain travelling along the nervous system.
13 Notice eating irons wrongly placed (11)
RESIGNATION: (EATING IRONS*).
16 Remiss to hammer out soaring German air (9)
FORGETFUL: FORGE (to hammer out) / TFUL (reversal of – i.e. “soaring” – LUFT. It’s the German word for the air that we breath).
18 Make firm points to clinch argument (7)
STIFFEN: S[outh], E[ast] and N[orth] around TIFF.
19 Reductive substitution English man used in mass medium (7)
METONYM: E / TONY in M (mass) / M (medium).
21 Set cryptically? That brings advantage! (3,2)
LEG UP: the idea is that “LEG UP” could be a cryptic clue for GEL (set).
22 Bad blood initially denied young heroine (5)
ALICE: [m]ALICE.
Sceptre and Crown
Must tumble down
Lines from a poem I learnt in school about 25 years ago which have stuck just because I distinctly remember our teacher telling us it was an example of metonymy.
A good quality puzzle and quite a challenge.
I think the parsing for 6D is SUP (drink) + RE (on) + MO (tick – short unit of time).
Paul G
Well, on to today’s!
Edited at 2018-10-13 03:28 am (UTC)
Edited at 2018-10-13 05:00 am (UTC)
I knew FIANNA FAIL vaguely but was not clear on the spelling so I was grateful for the wordplay and checkers.
ROCK SALMON used to be popular at fish ‘n’ chip shops at one time, but I guess not so these days as it was considered an inferior ‘product’ compared with cod or haddock.
Edited at 2018-10-13 04:25 am (UTC)
Edited at 2018-10-13 06:32 am (UTC)
Enjoyed: 26a PEEPING TOM, 22d ALICE.
The rest of the crossword took me 31 minutes, suggesting I rather struggled through it, though I can’t really say where the hold-ups were. FIANNA FAIL was my last in, and PEEPING TOM my most-enjoyed. Arguably a crossword celebrating iconic British naughtiness.
LOI was 19d I had no idea what a reductive substitution might be -the opposite of bringing on Peter Crouch after 70 minutes? Anyway I got Metonym and looked it up afterwards.
I did enjoy the struggle overall. David
Just one quibble – isn’t a reductive substitution a synecdoche? A metonym refers to an attribute rather than a part.