Across:
1 Group (S-ET) admits backing (= reversal indicator) church (Church of England = CE = -EC-) writing (from the 3Rs = -R-) (SECRET) at the start of 18 across (at the start of ‘secret ballot’ = SECRET),
4 Stock and barrels (GUN PARTS) destined for an assembly line of a major employer (army) (GUN PARTS),
9 Has an influence on the count (ABACUS), as what’s monitored is not in sodium carbonate (‘monitored’ is not in ‘sodium carbonate’ = sucaba = ABACUS),
10 Faith (IDEOLOGY) gets papers (ID- papers) from Spain (-E-) to go with a fair amount of (half of) technology (half of ‘technology’ = -OLOGY) (IDEOLOGY),
12 A sad piper (a sad piper) played (= anagram indicator) (a sad piper = DISAPPEAR) Peter out (DISAPPEAR),
13 Denies (denies) one (i) is missing (‘denies’ without ‘i’ = denes = NEEDS) essentials (NEEDS),
14 Cops the mysterious type (SECRET POLICE) concealed (SECRET) by monitor (POLICE) (SECRET POLICE),
18 Opening 14 across (opens ‘secret police’ = SECRET) for leading backbencher (leading ‘backbencher’ = B-) to give out (-ALLOT) (SECRET BALLOT) –Taoiseach would have no confidence in that sort of vote (SECRET BALLOT),
21 As the labourers see it, excellent (PLUM- job) head on pint (head on ‘pint’ = -P) (PLUMP) of stout (PLUMP),
22 Capable of making a scene (THESPIANS), as she paints (she paints = THESPIANS) all over the place (= anagram indicator),
24 Nothing unusual about (ORDINARY) old (O-) road (-RD-) to institute (-I-) that ran (ran) up (= reversal indicator) (ran = -NAR-) by yard (-Y) (ORDINARY),
25 Tip from opticians (‘tip’ from ‘opticians’ = ocians = CASINO) – avoid this if you don’t like taking risks (CASINO),
26 Users rip users rip = SURPRISE) off (= anagram indicator) (revelation (SURPRISE),
27 Laird removed from Alexandrine (‘laird’ removed from ‘Alexandrine’ = exanne = ANNEXE) wing (ANNEXE).
Down:
1 Careless (SLAPDASH) friends (pals = SLAP-) holding up (= reversal indicator) Dart (dart = -DASH) (SLAPDASH),
2 Student of comedy perhaps (CLASS ACT) is one to be admired (CLASS ACT),
3 Sally (sally/joke = -QUIP) follows (= positional indicator) engineer (E-) (EQUIP) by train (EQUIP),
5 Briefs (UNDERCLOTHES) a number of boxers (UNDERCLOTHES),
6 Raised from the ashes (Phoenix) without crossing (x) (‘Phoenix’ without ‘x’ = PHOENI-) intelligence agency (-CIA) (PHOENICIA) in old country (parts of Lebanon/Syria = PHOENICIA),
7 In order to remove Don (‘in order to’ remove ‘Don’ = irerto = RIOTER) from The Mob (RIOTER),
8 The most reserved (SHYEST) call for silence? (SH-) Certainly (-YES-), it’s time! (-T) (SHYEST),
11 Presumably, The Weather Girls recorded them (TEMPERATURES) with The Three Degrees and others (TEMPERATURES),
15 The Observer (EYE) intro (OPENER) (EYE OPENER) is a revelation (EYE OPENER),
16 Feel a bit (feel a bit = FLEA BITE) peculiar (= anagram indicator) in what’s an irritable spot (FLEA BITE),
17 Checks out The Hearing (OTOSCOPE) with old (O-) Count (count = tot) briefly (t) (‘tot’ without ‘t’ = -TO-) where there’s capacity (-SCOPE) (OTOSCOPE),
19 Spies (snoops) set up (= reversal indicator) (snoops = SPOONS) by those looking to stir things up (SPOONS),
20 Take out local (‘take out’ = MURDER) to back (= reversal indicator) Red Rum (Red Rum = MURDER),
23 It’s obvious (PLAIN) novice (learner = -L-) is in a bad way (P-AIN) (PLAIN).