Across:
8 Sound (VOLUME) produced by the bookmaker (VOLUME),
9 Czech (Czech) State (= homophone indicator) (‘Czech’ = ‘check’ = RESTRAIN) control (RESTRAIN),
10 Grave (TOMB) tips for the one-man band (tips/first letters for ‘The One-Man Band’ = TOMB),
11 Those in charge (EXECUTIVES) of the suits (the suits = EXECUTIVES),
12 Americans ignore sin (‘Americans’ ignore ‘sin’ = amerca = CAMERA) of film producer? (CAMERA),
14 Particular (SPECIFIC) mixed (= anagram indicator) spice (spice = SPECI-) for Indian cold starters (‘For Indian Cold’ starters = -FIC) (SPECIFIC),
15 Most of those in 21 down (most of ‘chiefs’ = CHIEF) and 11 across (‘executives’ = EXECUTIVES) (CHIEF EXECUTIVES) minding their own businesses presumably (CHIEF EXECUTIVES),
18 Sensational types (EMOTIONS) in Love/Hate (EMOTIONS),
20 First class (SELECT) choice? (SELECT),
22 Doesn’t make sense (IRRATIONAL) to one (I-) writing (from the 3Rs = -R-) with both feet on the ground (-RATIONAL) (IRRATIONAL),
24 Cold shower (HAIL) in Australia? Highly (in ‘austraLIA Highly uplifting’ = liah) uplifting! (= reverse indicator) (liah = HAIL),
25 Artist impressions (OUTLINES) of holiday (OUT-) bars (-LINES) (OUTLINES),
26 Former girlfriend (EX -) and recent partner (-WIFE) (EX-WIFE) no longer in The Union (EX-WIFE).
Down:
1 Conspirator tears off strip ('conspirator' tears off 'strip' = conaor = CORONA) from The Sun (CORONA),
2 Is not sensitive (NUMB) to open mic (open ‘Mic’ = -M-) in The Centre (nub = NU-B) (NUMB),
3 Model (= anagram indicator) elated (elated = DEL-ATE) over, for example (e.g. = -EG-), (DELEGATE), commission (DELEGATE),
4 Needs no introduction (p) to Free (‘purge’ without ‘p’ = URGE) Press (URGE),
5 Give one’s word (ASSURE) to answer (A-) Old Bob (‘old bob’ = shilling = -S-) to be certain (-SURE) (ASSURE),
6 Type of intelligence (ARTIFICIAL intelligence) produced by spies (-CIA-) in mischievous (= anagram indicator) airlift (airlift = ARTIFI-L) (ARTIFICIAL),
7 Prefer (LIKE-) sage (-WISE) (LIKEWISE) by the same token (LIKEWISE),
13 Let out (-VENT-) in the community (European Union = E-U-) with friend (-ALLY) (EVENTUALLY) sooner or later (EVENTUALLY)
14 Dismisses (SHEDS) female (SHE-) detective (-DS) (SHEDS),
16 Funny (HUMOROUS) organic matter (humus = HUM-US) found around summits with old rocky outcrops (summits with ‘Old Rocky Outcrops’ = -ORO-) (HUMOROUS)
17 Remained a mystery (UNSOLVED) why the crossword wasn’t filled in (UNSOLVED),
19 Red Baron’s (red barons = ONIONS) radars? (radars = ONIONS) If you know the answer, you have the local know-how! (you know your ONIONS),
21 Bosses (CHIEFS) ran away from franchise (‘ran’ away from ‘franchise’ = fchise = CHIEFS),
23 One of those on the plane (NOSE) is picked up in Bordeaux (Bordeaux wine / NOSE),
24 Sell door-to-door locally (HAWK) to half of Bray (hee-haw) (half of ‘hee-HAW = HAW-)? That’s fairly (half of) OK (half of ‘oK’ = -K)! (HAWK).