Across:
8 Month (OCT-) before (= positional indicator) Ireland (Republic of Ireland = -ROI) (OCTROI) could use this to raise old tax (OCTROI),
9 One drawing people (ANIMATOR) at a minor (at a minor) play (= anagram indicator) (at a minor = ANIMATOR),
10 A Mass (amass = KEEP) in Castle (KEEP),
11 Spreads the good news (EVANGELISM spreads the Good News Bible) for one of those trying to tell others about job? (telling others about the Book of Job? = EVANGELISM),
12 A mystery to some (ENIGMA) playing (= anagram indicator) in game (in game = ENIGMA),
14 Made up (MYTHICAL) legend (MYTH-) for one (-I-) that’s mostly (m) relaxed (‘calm’ without ‘m’ = -CAL) (MYTHICAL),
15 What to expect when you’ve finished walking the plank (A DROP IN THE OCEAN) doesn’t amount to much (A DROP IN THE OCEAN),
18 Engineering (E-) movement’s (movements = -MOTIONS) (EMOTIONS) strong feelings (EMOTIONS),
20 Lodge (INSERT) with enclosure? (INSERT),
22 Turns up (= reverse indicator), the foreign (‘the’ Spanish = las = SAL-) pitch (tar = -T -AR) overlooks resistance in Bastille? (-CELL-) (SALT CELLAR) With this in hand, press ahead to season! (SALT CELLAR),
24 Dog (TAIL) track? (TAIL),
25 Bordeaux (CLAR-ET) embraces fashionable (-IN-) (CLARINET) instrument (CLARINET),
26 Bits (PIECES) he’d removed from cheese dip (‘hed’ removed from ‘cheese dip’ = ceseip = PIECES).
Down:
1 Guard (SCREEN) detected (seen = S-EEN) getting hold of credit (-CR-) (SCREEN),
2 Release (DROP) the upsetting (= reversal indicator) extremes of police record (extremes of ‘POlice recoRD’ = pord = DROP),
3 Retail (retail) problem (= anagram indicator) (retail = LITERA-) at the opening of trading (opening of ‘Trading’ = -T-) for one (-I) (LITERATI) of those consumed by the books (LITERATI),
4 Swimming competition (GALA) on the banks of Gallipoli peninsula (on the banks of ‘GAllipoli peninsuLA’ = GALA),
5 Ad lib (WING IT) with funny guy (W- IT) swallowing gin (gin) cocktail (= anagram indicator) (gin = -ING) (WING IT),
6 The final parts of the stories (TAILPIECES) produced by 24 across (‘tail’ = TAIL-) and 26 across (‘pieces’ = -PIECES) (TAILPIECES),
7 Finish off (e) light fluffy dessert (‘mousse’ without ‘e’ = MOUSS-) also known as (Also Known As = -AKA) (MOUSSAKA) a Greek favourite (MOUSSAKA),
13 Spirits (ghosts = GHOST S-) from island (-TORY island) (GHOST STORY) – a novel idea for Halloween (GHOST STORY),
14 One of the subjects (MATHS) reviews (= reversal indicator) The Imposter (sham = MA-HS) outside the capital (‘The’ capital -T-) (MATHS),
16 Bedlam – an (Bedlam an) unstable (= anagram indicator) (Bedlam an = DAMNABLE) type that’s unpleasant (DAMNABLE),
17 Inscription (EPIGRAPH) produced by boss (= anagram indicator) happier (happier = EPI-RAPH) about golf (-G-) (EPIGRAPH),
19 Large quantities (OCEANS) at the end of 15 across (end of ‘a drop in the ocean’ = OCEAN-) going to school (-S) (OCEANS),
21 What the force did as a surprise (RAIDED) to remove spice from rice paddies (remove ‘spice’ from ‘rice paddies’ = raddie = RAIDED),
23 It’s after the deadline (LATE) for both sides in labour dispute (both sides in ‘LAbour dispuTE’ = LATE),
24 Leaves home (TREE) at present with no pants? (‘at present’ with no ‘pants’ = tree = TREE).