Across:
1 Cups from subtropics (‘cups’ from ‘subtropics’ = sbtroi = BISTRO) in nice restaurant (Nice/French restaurant / BISTRO),
4 Do they really hear if anyone’s there (PSYCHICS) or are they hearing things? (PSYCHICS),
9 Is alone (SINGLE) coming out of the chipper (SINGLE),
10 Collected (= anagram indicator) money (money = YEOM-N-) crossing a (-A-) railway (-R-) yard (-Y) (YEOMANRY) for the old volunteers (YEOMANRY),
12 Yank (TOW-) is not the first (‘Not’ the first = -N) working in court (CLERK) (TOWN CLERK) as an advisor to the corporation (TOWN CLERK),
13 Some manufacturer undermining (some ‘manufactuRER UNdermining’ = RERUN) stage again (RERUN),
14 Imagine (imagine/visualise = PICTURE) engineer (FRAME) (PICTURE FRAME) holding up the Liffey Swim, for instance (PICTURE FRAME is holding up Jack B Yeats’ The Liffey Swim),
18 It’s awkward (INCONVENIENT) for popular (IN-) novice (-N-) that is (i.e. = -IE-) taken in by religious institution (convent = -CONVE-NT) (INCONVENIENT),
21 One of The Doors (EXI-T) besieging lead singer (lead ‘Singer’ = -S-) (EXIST) to get a life? (EXIST),
22 Foreign politician (MP = M--P) welcomes support for swingers (tee) returning (= reverse indicator) (tee = -EET-) from popular (-IN-) summits getting used (summits ‘Getting Used’ = -G U-) (MEETING UP) to congregating (MEETING UP),
24 Stopping work (RETIRING) for revolting (= reversal indicator) ritual (rite = -ETIR-) in Ring (R-ING) (RETIRING),
25 Five (V-) paramilitaries (-IRA-) depart (-GO) (VIRAGO) from Spitfire (spitfire/bad-tempered = VIRAGO),
26 Unruly (RESTLESS) in Lounge (lounge/loll = REST-) and Takeaway (take away = -LESS) (RESTLESS),
27 Newscaster loses case (‘newscaster’ loses ‘case’ = newstr = STREWN) and is all over the place (STREWN).
Down:
1 Submarine (sub) rises (= reverse indicator) (sub = BUS) to the top of the sea (the top of the ‘Sea’ = S-) and heads (-TOPS) (BUS STOPS) for shelters at various stages (BUS STOPS),
2 Snack (SANDWICH) for heartless (t) sorcerer (witch) (‘wiTch’ without ‘t’ = -WICH) on the other side of (= position indicator) beach blanket (SAND-) (SANDWICH),
3 Characters in revolutionary (= reverse indicator) council erased (characters in ‘counCIL ERased’ = ciler = RELIC) from historical piece (RELIC),
5 End of autumn (end of ‘autumN’ = -N-) in The Mediterranean (sea = S-EA-) on weekend (‘weeK’ end = -K) – park (P-) and explore (-REVIEW) (SNEAK PREVIEW) what a critic gets to see first! (SNEAK PREVIEW),
6 She gets shot presumably (CAMERAMAN) working as a journalist (CAMERAMAN),
7 Send to Coventry (IGNORE) from wild (= anagram indicator) region (region = IGNORE),
8 Cutting to pieces (slaying) without large (l) (‘slaying’ without ‘l’ = SAYING) saw (saw/proverb = SAYING),
11 New issues (DEVELOPMENTS) to improve (DEVELOP-) worker’s (workers = -MEN-) shirt (-T- shirt) with top-stitching (top ‘Stitching’ = -S) (DEVELOPMENTS),
15 Clip (n) of twist (turn) (‘turn’ without ‘n’ = -TUR-) in annual (annual) adaptation (= anagram indicator) (annual = UNNA-AL) (UNNATURAL) that’s peculiar (UNNATURAL),
16 Top bioterrorist (top ‘Bioterrorist’ = B-) finds criminal (= anagram indicator) dealer (dealer = -EL-RADE) around great (-G-) (BELGRADE) European capital (BELGRADE),
17 Resign (STEP DOWN) from the stage (STEP) in Northern Ireland (DOWN) (STEP DOWN),
19 Blind panic (TERROR) on first tee (first ‘Tee’ = T-) leads to inaccuracy (-ERROR) (TERROR),
20 No romance in South American (no ‘romance’ in ‘South American’= suthia = HIATUS) break (HIATUS),
23 Dopey is one (IDIOT) gnome leaving in good time (‘gnome’ leaving ‘in good time’ = iodti = IDIOT).