Across:
1 Fail to move steadily (totter / DODDER) running through Dublin (DODDER river),
4 Detectives’ (DIs = DIS-) line-up (-ORDER) (DISORDER) for breach of the peace (DISORDER),
9 Contagious enthusiasm (FEVER-) for endless (end ‘lesS’ = -S) (FEVERS) high temperatures (FEVERS),
10 A (A-) top sketch (top ‘Sketch’ = -S-) that’s second to none (-BEST-) from Duck (-O-) Soup with lead (‘Soup’ with lead = -S) (ASBESTOS) producing material that’s considered very dangerous (ASBESTOS),
12 Where to view The Penguin (ANTARCTIC) in the Deep South? (ANTARCTIC),
13 Femme fatale (SIREN) on the outskirts of San Sebastian (on the outskirts of ‘San sebastiaN = S-N) getting to grips with hot temper (-IRE-) (SIREN)
14 Cher (Cher = CH- -ER) catches that is (i.e. = -IE-) loud music (forte = -F) associated with lament (lament = MOURN-) (CHIEF MOURNER), as she’s the one most familiar with The Dead (CHIEF MOURNER),
18 Avoiding (SIDESTEPPING) chips, for instance (SIDE-), with pints? Peg (pints peg) Rock! (= anagram indicator) (pints peg = -STEPPING)! (SIDESTEPPING),
21 Advantage (ASSET) of rearranging (= anagram indicator) seats? (seats = ASSET),
22 Unoccupied (FREE) by Canada, for instance (STATE) (FREE STATE), or US in the past? (us in the past/Ireland = FREE STATE),
24 Barman (BL-) is (-IS-) going to party (Sinn Féin = -SF-) at university (University of Limerick = -UL) (BLISSFUL) in raptures (BLISSFUL),
25 It’s discussed at the bar (law) briefly (w) (‘law’ without ‘w’ = LA-) – Peter’s out (-DIES) (LADIES) with noblewomen? (LADIES),
26 Tops of nerve plexus (tops of ‘Nerve Plexus’ = -NP-) in damaged (= anagram indicator) cheeks (cheeks = HE- -ECKS) (HENPECKS) and that annoys terribly (HENPECKS),
27 Opens 14 across (opens ‘chief mourner’ = CHIEF-) at school (-S) (CHIEFS) for those in charge (CHIEFS).
Down:
1 Refusal to obey (DEFIANCE) English (-E-) and Irish men (Irish 'men' = fir) mostly (r) ('fir' without 'r' = -FI-) in Charleston (dance = D-ANCE) (DEFIANCE),
2 Veto (veto) organised (= anagram indicator) (veto = -OVET-) in The House (D-AIL) (DOVETAIL) leads to accord? (DOVETAIL),
3 A slip (ERROR) leads to a horror (terror) striking the head (t) (‘terror’ without ‘t’ = ERROR),
5 It’s popular (IN-) with those employed in the finance business (-SECURITIES) (INSECURITIES) or concerns that don’t give you confidence (INSECURITIES),
6 Out at night, more so than usual (OVERSLEEP) – it’s what she might do awaiting the handsome prince (Sleeping Beauty OVERSLEEP),
7 Hampers (DETERS) site off side street (‘site’ off ‘side street’ = desret = DETERS),
8 Begrudge (RESENT) press agent releasing gasp (‘press agent’ releasing ‘gasp’ = resent = RESENT).
11 The good fortune (STROKE OF LUCK) of a hole in one presumably (STROKE OF LUCK),
15 It’s not obvious to me (FAIL TO SEE) Miss (miss = FAIL TO SEE),
16 Settle (FINALISE) one (-I-) consumed by big exams (finals = FINAL-S-) with note (music note -E) (FINALISE),
17 Ways out (EGRESSES) for press agencies dismissing panic (‘press agencies’ dismissing/without ‘panic’ = ressgees = EGRESSES),
19 Graduate (-BA-) in capital (cash = -CAS-H) (CASBAH) with citadel (CASBAH),
20 Give out to (ASSIGN) young woman (lass) losing the head (l) (‘lass’ without ‘l’ = ASS-) up (= reverse indicator) north (NI = -I-N) around summit of Gullion (summit of ‘Gullion’ = -G-) (ASSIGN),
23 Local’s drugs haul (STASH) found in street (ST-), dropped by smoker (-ASH) (STASH).