Across:
1 Key (music key -A-) found in untidy (= anagram indicator) pocket (pocket = P-CKET O-) with fag end (‘faG’ end = -F) and watch (SEE-) given to detective? (Detective Sergeant = -DS) (PACKET OF SEEDS) – did someone in the plot plant them? (PACKET OF SEEDS),
10 Bill (AD-) for sunscreen (-VISOR) (ADVISOR) for coach (ADVISOR),
11 Square (-T- square) in Cairo (Cairo = CROA-I-) built (= anagram indicator) with American capital (‘American’ capital = -A) (CROATIA) – it’s bound to remind one of split (CROATIA / Split),
12 Family (KIN-) dispute lead (‘Dispute’ lead = -D) (KIND) by Clement? (clement/merciful = KIND),
13 The belief is (CREDO), there’s no gas to be found in God’s acre (no ‘gas’ to be found in ‘Gods acre’ = odcre = CREDO),
15 Rugby players (PACK) sort of popular with all sides today (PACK on four sides of today’s grid),
17 Inseparable (ONE is inseparable) from Horatio Nelson? (from ‘HoratiO NElson’ = ONE),
19 Ruffle someone’s feathers (NEEDLE) with what’s on the record player (NEEDLE),
21 Barman (Bachelor of Law = BL-) with a German name (-OTTO) (BLOTTO) is wasted (BLOTTO),
22 Rode Red (Rode Red) Rum (= anagram indicator) (Rode Red = ORDERED) to put in place (ORDERED),
23 Head off (w) to war (‘war’ without ‘w’ = AR-) on unfinished (l) waterway (‘canal’ without ‘l’ = -CANA) (ARCANA) with mysterious types (ARCANA),
25 Presumably this is how Dracula will cut his fangs? (TEETHE) Of course (TEE- on golf course), it leads to hellish evil! (leads ‘To Hellish Evil’ = -THE) (TEETHE),
27 One of the family (sister = SIS) taken in by Ellis Island (taken in by ‘ElliS ISland’ = SIS),
29 It’s a measure (UNIT) of trade unionists lacking adroitness (‘trade unionists’ lacking ‘adroitness’ = unit = UNIT),
30 Sets (PACKS) jams? (PACKS),
31 Amidst upsetting (= reversal indicator) thumb motion (amidst upsetting ‘thumB MOTion’ = bmot = TOMB) in the dead centre (TOMB),
34 Put one’s hands together (CHERR-) for Number 10 (-IO) (CHERRIO) – having said that, will they Leave? (CHEERIO),
35 Going over a map (TRACING) in car (model T-) in Rush (-RACING) (TRACING),
36 Criminal gang (PACK OF THIEVES) put away (PACK) for taking ring (O-) to offend (‘ofF’ end = -F) those supplying fences (THIEVES) (PACK OF THIEVES).
Down:
2 Caught (-C-) in Nevada (Nevada) working (= anagram indicator) (Nevada = ADVAN-E) (ADVANCE) with money up front (ADVANCE),
3 Some characters in Donnybrook issued (some characters in ‘DonnybrooK ISSued’ = KISS) a welcome that’s very informal (KISS),
4 Celebrated in Ring with the red cape (TORERO bullfighter) and in Ballitore romance (in ‘BalliTORE ROmance’ = TORERO),
5 Features (FAC-E) around advertisement (-AD-) (FACADE) is all for show (FACADE),
6 Not best pleased (sore) upsetting (= reversal indicator) (sore = EROS) lover (EROS),
7 Bone (-T- bone) found in stew (= anagram indicator) carted (carted = DE-RACT) (DETRACT) out of Takeaway? (take away/lessen = DETRACT),
8 Local carrying piece (PACKING a gun), article (A) and clip (PUNCH) (PACKING A PUNCH) is capable of flooring an opponent (PACKING A PUNCH),
9 Prepares to leave (PACKS ONE’S BAGS) bands (PACKS) and individuals (ones = ONE’S) to chat (gab = BAG-) up (= reversal indicator) lead singer (lead ‘Singer’ = -S) (PACKS ONE’S BAGS),
14 Characteristic of a particular area (ENDEMIC) around (= reversal indicator) Clare (CE = E-C) containing denim (denim) production (= anagram indicator) (denim = -NDEMI-) (ENDEMIC),
16 No grub in lounge bar (no ‘grub’ in ‘lounge bar’ = lonea = ALONE) that’s isolated (ALONE),
18 Dealer (dealer) clears a (a) (‘dealer’ without ‘a’ = deler = ELDER) part of the forest (ELDER),
20 1970s America, for instance (ERA), encapsulated by Deliverance (encapsulated by ‘DelivERAnce’ = ERA),
21 Back (BET) in the Globe Theatre (in the ‘GloBE Theatre’ = BET),
24 Foolish fancy (CHIMERA) of that man (-HIM-) in hospital (-ER-) in California (C-A) (CHIMERA),
26 Drag (tow) up (= reversal indicator) (tow = -WO-T-) in magazine (Time magazine = T-IME) (TWO-TIME) what cheat did to lover (TWO-TIME),
27 Remove (SAW OFF) spy in the past (SAW) from old (O-) party (Fianna Fáil = -FF) (SAW OFF),
28 No matter – it’s not part of shock treatment (‘no matter’ it’s not part of ‘shock treatment’ = SKETCH) by design (SKETCH),
32 Trackers lose cars (‘trackers’ lose ‘cars’ = tker = TREK) in a long arduous journey (TREK)
33 In part, consider a venture (in part ‘consideR A VEnture’ = RAVE) that appeals to dancers (RAVE).