Across:
1 A steady flow (STREAM) from master (master = STREAM) criminal (= anagram indicator),
4 Is (IS-) left (-L-) to roam (wander) starting off (w) (‘wander’ without ‘w’ = -ANDER) (ISLANDER) in Man of Aran (ISLANDER),
9 Constabulary withdraws bounty (‘constabulary’ withdraws ‘bounty’ = scalar = RASCAL) for cheeky chappie (RASCAL),
10 Detective (-PI-) in today’s (todays = DYSTO-A) rag (= anagram indicator) (DYSTOPIA) depicts how bad things were in 1984, for example (George Orwell’s 1984, for example depicts DYSTOPIA),
12 Finish (POLISH OFF) with European (POLISH) on holiday (OFF) (POLISH OFF),
13 Some algorithm or secret (some ‘algorithm or secret’ = MORSE) code (MORSE),
14 How does one decide who is the best comedian (BATTLE OF WITS) as Behan and Beckett make a contest of it (BATTLE OF WITS),
18 They hold all the documentation (BULLDOG CLIPS) for Fiat (BULL-) and Rover (-DOG) with trims (CLIPS) (BULLDOG CLIPS),
21 Kept away from sketch map (‘kept’ away from ‘sketch map’ = schma = CHASM) of Gulf (CHASM),
22 Rib (KID-) and head taken (s) from fish (‘snapper’ without ‘s’ = -NAPPER) (KIDNAPPER) – the person who took them illegally wants what amounts to a ransom to give them back (KIDNAPPER),
24 Material (CORDUROY) is cut for delivery (umbilical CORD-) to your (your = -UROY) building (= anagram indicator) (CORDUROY),
25 Nine released from East Indian (‘nine’ released from ‘East Indian’ = astdia = STADIA) venues (STADIA),
26 Expect one to get this, for example (PROPHESY), from something Jeremiah said (PROPHESY of Jeremiah, the prophet),
27 French (F-) paper (paper = -RAPPE) laid out (= anagram indicator) (FRAPPE) and consumed in the parlour (ice/frozen FRAPPE drink).
Down:
1 Have just enough in one’s locker (SCRAPE BY) to beat (= anagram indicator) pacy Serb (pacy Serb = SCRAPE BY),
2 Determined (RESOLUTE) and right (R-) to head off (p) from capital (capital/money = ‘peso’ without ‘p’= -ESO-) with State’s (states = homophone indicator) spoils of war (‘loot’ = ‘lute’ = -LUTE) (RESOLUTE),
3 Bedouins (ARABS) returning (= reversal indicator) and hidden in Sands Bar alehouse (hidden in ‘Sands Bar alehouse’= sbara = ARABS),
5 Request when saying goodbye perhaps (SAY A FEW WORDS) to keep it short, in a manner of speaking (SAY A FEW WORDS),
6 Unconscious (AUTOMATIC) runner (-MAT-) found behind (= positional indicator) car (AUTO-) from independent (-I-) college (-C) (AUTOMATIC),
7 Make tracks (DEPART) for Playback (= reversal indicator) taped (taped = DEPA-T) around end of December (end of ‘December’ = -R-) (DEPART),
8 Put off departure (‘put’ off ‘departure’ = dearre = READER) from the library (READER),
11 The man upstairs (GOD) just (ONLY) recognises (KNOWS) (GOD ONLY KNOWS) what the future holds, as the saying goes (GOD ONLY KNOWS),
15 Show off (LOUDMOUTH) deep (LOUD-) part of the river (-MOUTH) (LOUDMOUTH),
16 With the clip (r) of The Fly (‘zipper’ without ‘r’ = ZIPPE-) with Con (dupe) Short (e) (‘dupe’ without ‘e’ = -D UP) (ZIPPED UP) – that’s a complete wrap! (ZIPPED UP),
17 Menus are (menus are = USERNAME) wrong (= anagram indicator) for securing the online service (USERNAME),
19 No room in comic opera (no ‘room’ in ‘comic opera’ = cicpea = ICE CAP) for cold type from summit (ICE CAP),
20 Bob (HAIRDO) runs the committee (chair) without leader (c) (‘chair’ without ‘c’ = HAIR-) from party (-DO) (HAIRDO),
23 On the trail of (AFTER) Sue from Features (‘Sue’ from ‘Features’ = featr = AFTER).