Across:
1 One of The Blades (one of the blades = DAGGER) backed (= reversal indicator) most of the music coming from Jamaica (most of the 'reggae' = regga = -AGGER) with depth (-D) (DAGGER),
4 One (I-) church (Church of England = -CE) reporter (CUB- reporter) with desk at the centre (‘dESk’ at the centre = -ES) (ICE CUBES) of the blocks of water coolers? (ICE CUBES)
9 Find it (-IT-) in corn (corn = C-RON), soup (= anagram indicator) (corn = C-RON) (CITRON) and ingredient for lemonade (CITRON),
10 A range of spirits (EMOTIONS) in one moist (one moist) bake (= anagram indicator) (one moist = EMOTIONS),
12 The Chosen One (APPOINTEE) produced opening preamble (opening ‘Preamble’ = -P-) – what’s the objective (-POINT-) taking ecstasy (-E-) in A&E? (A-E) (APPOINTEE),
13 Some remarkable aversion (some ‘remarkabLE AVErsion’ = LEAVE) to what holidaymakers are liable to take (take LEAVE)
14 Measurements from an experiment (OBSERVATIONS) in a bistro’s oven (a bistro’s oven) mixed-up (= anagram indicator) (a bistro’s oven = OBSERVATIONS),
18 Suggests it’s not compulsory (NO OBLIGATION) to jeer (boo) backward (= reversal indicator) (boo = -O OB-) leaders left in Government (leaders ‘Left In Government’ = -LIG-) in Germany, for one (nation = N- -ATION) (NO OBLIGATION),
21 Turns up (= reverse indicator), most of (e) the country (Eire) (‘eirE’ without ‘e’ = eir = -RIE-) taken in by church (Roman Catholic = RC = C-R) (CRIER) broadcaster in the past (Town CRIER),
22 Manage (RUN-) a (-A-) number of events in Ring (number of events in boxing ring = -BOUTS) (RUNABOUTS) with cars (RUNABOUTS),
24 Cover (FILM) for cold (C-) mouthy type (-LIP) (FILM CLIP) in trailer (trailer/preview = FILM CLIP),
25 Serving up (= reversal indicator), regrettably (alas = -SALA) for Dawn (morning = am = MA-) (MASALA), something spicy (MASALA),
26 The worst of the worst (GROSSEST) gets Ross (gets Ross) drunk (= anagram indicator) (gets Ross = GROSSEST),
27 Iron (Fe = F-E) found around River (River -LEE-) Corrib on top of (‘Corrib’ on top of = -C-) (FLEECE) sheep’s wool (FLEECE).
Down:
1 The Speaker in relation to PA (DICTATOR) has absolute control (DICTATOR),
2 Theatre (GATE- Theatre) appointment (-POST) (GATEPOST) is a mutual confidant of you and me (GATEPOST / “between you and me and the gatepost”),
3 Ran away from Caroline (‘ran’ away from ‘Caroline’ = colie = E COLI) producing a bad strain (E COLI),
5 Contests (COMPETITIONS) firm (CO-) is getting 1000 (-M-) written protests with signatures (-PETITIONS) (COMPETITIONS),
6 Persian (CAT-) is briefly (e) isolated (‘alone’ without ‘e’ = -ALON-) on one (-I-) summit on archipelago (summit on ‘Archipelago’ = -A) (CATALONIA) in Spain (CATALONIA),
7 A brogue, but not the type you hear (BROGAN shoe) in lively (= anagram indicator) Bangor (Bangor = BROGAN),
8 Mass hysteria ignoring Sharia (‘mass hysteria’ ignoring ‘Sharia’ = mssyte = SYSTEM) practice (SYSTEM),
11 It aids drinking (STRAW-) sir? Beer (sir beer = -BERRIES) mixed (= anagram indicator) (STRAWBERRIES) with fruit! (STRAWBERRIES),
15 What Thatcher is responsible for (ROOF) tortures (RACKS) (ROOF RACKS) those having to bear the baggage for the long road perhaps (ROOF RACKS),
16 Mimic (SIMULATE) is (is) upset (= reverse indicator) (is = SI-) by strange (= anagram indicator) amulet (amulet = -MULATE) (SIMULATE),
17 Popular (IN-) answer (A) and tweet (tweet/say = STATE) (IN A STATE) is edgy (IN A STATE),
19 Cork (-C-) in Ireland (Ireland domain = .ie = I-E) has party (Fine Gael = F-G) around middle of October (middle letter of ‘octOber = -O-) (ICE FOG) in winter mist (ICE FOG),
20 Old foreign market (RIALTO is the old mercantile quarter of Venice) in Dublin? (RIALTO),
23 Below par without Poe (‘below par’ without Poe’ = blwar = BRAWL) in Donnybrook (BRAWL).