Across:
8 Finishes 15 across (finishes “newspaper column” = COLUMN) with row (COLUMN),
9 Labour (WORK-) provided this type of service (-ROOM service) (WORKROOM) in office (WORKROOM),
10 A stretch (SPAN) locked up in Hispaniola (locked up in “Hispaniola” = SPAN),
11 It’s a boon for a thief (OPEN WINDOW) to unlock (OPEN) most of (s) the operating system (“Windows” = WINDOW) (OPEN WINDOW),
12 Trouble (WAR-) about (-RE-) first novel (first “novel” = -N-) (WARREN) set in The Maze (maze = WARREN),
14 VAT files (VAT files = FESTIVAL) lost (= anagram indicator) – that’ll be some celebration! (FESTIVAL),
15 It’s a matter of opinion (NEWSPAPER COLUMN) for guardian (Guardian NEWSPAPER) offering support (support/pillar = COLUMN) (NEWSPAPER COLUMN),
18 Turns up (= reversal indicator), Split (split = depart = -TRAP-ED) harbour park (-P-) is close to school (S-) (STRAPPED) with cash-flow problem (STRAPPED),
20 Turn one’s back on (INSULT) sunlit (sunlit = INSULT) complex (= anagram indicator),
22 Work out (CALCULATE-), starting on dumbbells (starting on “dumbbells” = -D) (CALCULATED) – it’s how they got the figures? (CALCULATED),
24 Fix (MEND) sample of beam-ends (sample of “beam-ends” = MEND),
25 Resigned oneself (ACCEPTED) to go along with (ACCEPT-) writer (-ED) (ACCEPTED),
26 Movement (= anagram indicator) rioted (rioted = EDITOR) and did a job on 15 across (EDITOR did a job on “newspaper column”).
Down:
1 Local criminal (hood) isn’t finished (d) (“hood” without “d” = HOO-) putting pressure (-P-) on American city (-LA) (HOOPLA) creating excitement (HOOPLA),
2 Convert (TURN) gets no rehab for heartburn (no “rehab” for “heartburn” = rtun = TURN),
3 Doesn’t cater for the dreamers (INSOMNIA) who won’t let sleeping dogs lie? (INSOMNIA),
4 It’s sentimental (TWEE) to most of (t) Twitter (“tweet” without “t” = TWEE),
5 Donnybrook’s (donnybrooks = BRAWLS) cup goes missing in pub crawls (“cup” goes missing in “pub crawls” = brawls = BRAWLS),
6 Code of ethics (PRINCIPLES) for travelling (= anagram indicator) reps in clip (reps in clip = PRINCIPLES),
7 The advice of the man upstairs (DO NO HARM) is crucial for the Hippocratic oath (DO NO HARM),
13 Her career’s (her careers = RESEARCHER) damaged (= anagram indicator) by investigator (RESEARCHER),
14 Discipline (FIELD) of a group of runners (FIELD),
16 Cast a spell over (put into a trance/beguile = ENTRANCE) writer (pen) heading off (p) (“pen” without “p” = EN-) from state down under perhaps? (-TRANCE) (ENTRANCE),
17 The issue (CHILDREN) of wild (= anagram indicator) lichen (lichen = CHIL-EN) found around drive (-DR-) (CHILDREN),
19 Cultured (POLITE) bar (POL-E) possesses it (-IT-) (POLITE),
21 The Capital (LONDON) opens late one night (opens/first letters of “late one night” = LON-) for one of those in the Mafia (-DON) (LONDON),
23 Crash (= anagram indicator) diet (diet = TIDE) – the current trend suggests one has a yo-yo effect (in and out = yo-yo effect = TIDE),
24 The most important (MAIN) part of pro-forma invoice (part of “pro-forma invoice” = MAIN).