Across:
1 Holding the top three places (for winners = PODIUM) for opium (opium = PO-IUM) production (= anagram indicator) around delta (-D-) (PODIUM),
4 Sour (OFF-) milk – the colour of (-WHITE) (OFF-WHITE) which has a greyish yellow tinge? (OFF-WHITE),
9 Respected (respected/eminent = AUGUST) heads of army units (heads of ‘army units’ = AU-) and air force (-GUST) (AUGUST),
10 Small (S-) horse (pony = -YNOP-) – Boomerang’s (= reversal indicator) relative (-SIS), (SYNOPSIS) in summary (SYNOPSIS),
12 Talent spotter (SCOUT) finds half of 26 across (half of ‘road sign’ = SIGN) (SCOUT SIGN) offering three-finger salute (SCOUT SIGN),
13 Most of (n) the piece (‘gun’ without ‘n’ = GU-) on American city (-LA-) golf (-G) (GULAG) camp held the Russians captive (GULAG),
14 Short (t) break (‘bust’ without ‘t’ = BUS) in the concert hall (CONDUCTOR) (BUS CONDUCTOR) for old ticket seller going from stage to stage (BUS CONDUCTOR going from bus stage to bus stage),
18 Recognise (FINGER-) pictures in art gallery that aren’t the originals (-PRINTS) (FINGERPRINTS) collected by Constable (collected by constable/police = FINGERPRINTS),
21 Greek taken out of Great Lakes (‘Greek’ taken out of ‘Great Lakes’ = atlas = ATLAS) has a lot on his shoulders (in mythology, ATLAS has the weight of the world on his shoulders),
22 That can be avoided (AVERTABLE) with late brave (late brave = AVERTABLE) move (= anagram indicator),
24 You’ll find this in 21 across, for instance (CAMBODIA found in ‘atlas’), and in Asia (CAMBODIA),
25 10K (-RUN-) in Belgium (B-E-) is one (-I) (BRUNEI) for Malaysian neighbour (BRUNEI),
26 Course (ROAD) for recruit (SIGN) (ROAD SIGN) plays a big part in traffic management (ROAD SIGN),
27 School (S-) trip (-TRE-K) oversteps a (-A-) (STREAK) line, in a colourful way (STREAK).
Down:
1 Paris (Paris = PRAIS-), excited (= anagram indicator) by Oriental (east = -E) state (=homophone indicator) honey producer (“bee” = “be” = BE) (PRAISE BE), expresses relief (PRAISE BE),
2 For party, (DO-), for government (-G-) and for parliament (-HOUSE) (DOGHOUSE) – Rex is bound to be there (DOGHOUSE),
3 Deputies die off (‘deputies’ ‘die’ off = putes = UPSET) and it causes distress (UPSET),
5 Runner (CARPET) initially (= positional indicator) is going fast (FLYING) (FLYING CARPET) and the skies the limit if this takes off according to legend (FLYING CARPET),
6 The devil (WRONGDOER) in Justice (injustice = WRONG-) is a person of action (-DOER) (WRONGDOER),
7 Turn one’s back on (INSULT) sunlit (sunlit = INSULT) complex (= anagram indicator),
8 It’s standard (standard/flag = ENSIGN) to conceal children’s ignorance (to conceal ‘childrens ignorance’ = ENSIGN),
11 Résumé (BIO-) is demeaning (-DEGRADING) (BIODEGRADING) those working in waste management (BIODEGRADING),
15 They’re left out (OMISSIONS) for ducks (Os = O-S) outside religious building (-MISSION-) (OMISSIONS),
16 Training (= anagram indicator) begonia (begonia = ON A BI-GE) around bottom of garden (bottom of ‘garden’ = -N-) (ON A BINGE) going from bar to bar (ON A BINGE),
17 Players (cast) lose the head (c) (‘cast’ without ‘c’ = AST-) at end of game (at end of ‘game’ = -E-) with Hazard (-RISK) (ASTERISK) – could it alert you to a footnote in match report, for instance (ASTERISK),
19 Learn (learn = LAN-ER) exercise (= anagram indicator) around club (-C-) (LANCER) from one of those old fighters (LANCER),
20 Manual (manual = ALUMNA) work (= anagram indicator) for female graduate (ALUMNA),
23 Count (count/add = T-OT) admits blood type (-A-) is right (-R-) (TAROT) – it’s from the hand of the fortune-teller (TAROT card).