Across:
1 Paramilitaries (Ulster Freedom Fighters = -UFF-) arrested by detective (PI = P-I-) closing investigation (closing 'investigatioN' = -N) (PUFFIN) for bird you might recognise from The Bill (PUFFIN is a bird with a brightly coloured triangular bill),
4 Street (WAY-) is a great distance (-FAR-) from hospital (-ER) (WAYFARER) for one going on foot (WAYFARER),
9 Shipmates ignore map (‘shipmates’ ignore ‘map’ = shites = THESIS) produced by scholar in final year (THESIS),
10 Sam’s epic (Sam epic) adaptation (= anagram indicator) (Sam epic = ESCAPISM) appeals to those living the dream (ESCAPISM),
12 English (E-) priest (Rev) upsets (= reversal indicator) (Rev = -VER-) Olive (olive green = -GREEN) (EVERGREEN) and Laurel (laurel = EVERGREEN),
13 Remain out of air terminal (‘remain’ out of ‘air terminal’ = aitrl = TRIAL) for pilot study (TRIAL),
14 500 (Roman 500 = D-) subject to The Draft (-AIRY) could be experts in their field (FARMERS) (DAIRY FARMERS) or stockholders around Jersey? (DAIRY FARMERS),
18 Monitor (SCREEN-) bookmaker (-WRITER) (SCREENWRITER) who produced The Script? (SCREENWRITER),
21 Concealed by Pietro Badoglio (concealed by ‘pieTRO BAdoglio’ = troba) going back (= reversal indicator) (troba = ABORT) to cancel launch (ABORT)
22 A (A-) mountaintop (‘Mountain’ top = -M-) of heather (-ERICA-) leads to natural spring (leads to ‘Natural Spring’ = -NS) (AMERICANS) coming from Wyoming, for example (AMERICANS),
24 Political plans perhaps (ROAD MAPS) for pro-Adams (pro-Adams) shift (= anagram indicator) (pro-Adams = ROAD MAPS),
25 Soldier (RANGER) in regiment (R-) from Red State? (-ANGER) (RANGER),
26 One of those behind bars (LICENSEE) is not the first (‘Not’ the first = -N-) to follow (= positional indicator) parasites (LICE-) for notice (-SEE) (LICENSEE),
27 CID leaving residence (‘CID’ leaving ‘residence’ = resene = SERENE) in Pacific (pacific/peaceful = SERENE).
Down:
1 Bonus for the waiter (tip) serving up (= reversal indicator) (tip = PIT-) the frothy tops on stout (-HEADS) (PITHEADS) from those with access to the home of The Black Stuff (PITHEADS),
2 Worry (worry/fret = FRE-T-) over points (compass points ‘North-East’ = -NE-) to get into top (‘Into’ top = -I-) college (-C) (FRENETIC) – it’s all go in a wild, uncompromising way (FRENETIC),
3 Sickening without Ken’s (‘sickening’ without ‘Kens’ = icing = ICING) topping (ICING),
5 Daydreaming (ABSENT-MINDED) when not in school? (‘absent’ = ABSENT-) Took umbrage with that! (-MINDED) (ABSENT-MINDED),
6 Father (F-R) consumes coffee (-LATTE-) with a fair amount of (half) care (half of ‘caRE’ = -RE-) (FLATTERER), for example, telling the barista dishonestly, it’s the best cup ever (FLATTERER),
7 An Iris (an iris) variety (= anagram indicator) (an iris = RAISIN) with fruit that’s typically dried (RAISIN),
8 Discover something illicit locally (RUMBLE) produced by one from Melbourne (‘one’ from ‘Melbourne’ = melbur = RUMBLE),
11 What a role model could do (SET AN EXAMPLE) for Irishman (Sean = SE- AN) over time (-T), when divorcee (EX-) has more than enough (-AMPLE) (SET AN EXAMPLE),
15 Church (-CH-) consumed by foreign (anagram indicator) amnesty (amnesty = YA-TSMEN) (YACHTSMEN) for sailors (YACHTSMEN),
16 Take someone’s breath away? (STRANGLE) Go out in strong gale! (‘go’ out in ‘strong gale’ = strngale = STRANGLE),
17 Maintain (PRESERVE) park (P-) for one of those on bench (extra player/sub on bench = -RESERVE) (PRESERVE),
19 Watch (PATROL) pâté (pate) and roll (roll) – neither is finished? (‘e’ + ‘l’) (‘pâté’ and ‘roll’ without ‘e’ and ‘l’ = PAT+ ROL) (PATROL),
20 Turns up (= reverse indicator), agency (CIA = -AIC) starts spreading old mistakes (opens with ‘Same Old Mistakes’ = som = MOS-) (MOSAIC) – therein lies the pattern (MOSAIC),
23 Painting (IMAGE) of Frenchman (Monsieur = -M-) at the bar (Attorney General = -AG-) in Ireland (Ireland domain = .ie = I-E) (IMAGE).