Across:
8 Shock (TRAUMA) of opening tipple (opening ‘Tipple’ = T-) for a rum (a rum) cocktail (= anagram indicator) (a rum = -RAUM-) at start of the afternoon (start of ‘Afternoon’= -A) (TRAUMA),
9 Use on USA (use on USA) trip (= anagram indicator) (use on USA = NAUSEOUS) as feeling sick (feeling sick = NAUSEOUS),
10 There are no vines in Nashville (there are no ‘vines’ in ‘Nashville’ = ahll = HALL) synonymous, for instance, with the chateau’s entry level (HALL),
11 Sworn statement (DEPOSITION) of French (‘of’ French = DE-) stance (-POSITION) (DEPOSITION),
12 Old European (THEBAN) prohibition restricting the players switching codes in past (‘the ban’ prohibited switching codes/sports = THE BAN),
14 Bring up the issue (bring up/raise the issue/children = PARENTED) of raise (PARENT-) with writer (-ED) (PARENTED)
15 Test (RUN AN EXPERIMENT) pilot? (RUN AN EXPERIMENT),
18 Nerve gas (nerve gas) produced by (= anagram indicator) (nerve gas = AVENGERS) agents of retribution (AVENGERS),
20 Those legally in possession (OWNERS) of home taken away from horsewomen (‘home’ taken away from ‘horsewomen’ = rsewon = OWNERS),
22 It’s disconcerting (DISTURBING) playing (= anagram indicator) tiring Dubs (tiring Dubs = DISTURBING),
24 Basic research starts and ends (‘BAsic researCH’ starts and ends = BACH) with composer (BACH),
25 For the German drinkers (BEER HALL) in (in) state (= homophone indicator) (‘in’ = ‘inn’ = BEER HALL),
26 Say yes to (ACCEPT) investor getting out of contraceptives (‘investor’ getting out of ‘contraceptives’ = ctacep = ACCEPT).
Down:
1 Bring up (BROACH) British (B-) swimmer (-ROACH fish) (BROACH),
2 Religious edict (BULL) located in Istanbul library (BULL found in ‘istanBUL Library’),
3 Sorry I missed that (PARDON ME) free (PARDON) motorway (M-) to Spain (-E) (PARDON ME),
4 Clip (SNIP) of Bolt’s (bolts/pegs = pins) retirement (= reversal indicator) (pins = SNIP),
5 One of those on The Screen (CURSOR) from Rising (= reverse indicator), Revenue Commissioners (Revenue On-Line Service = ROS = -SOR) and old police force (Royal Ulster Constabulary = RUC = CUR-) (CURSOR),
6 Chap taking a risk (BETTING MAN) by losing the head (v) checking the reliability of (vetting) (‘vetting’ without ‘v’ = -ETTING) Frenchman (Monsieur = -M-) in bar (bar/ban = B- -AN) (BETTING MAN),
7 For example, Russian (EUROPEAN) money (EURO-) given to one of The Greens (-PEA-) by Pole (North Pole = -N) (EUROPEAN),
13 A follower (B- follows ‘a’) gets to hold the crown (reign), in a manner of speaking (= homophone indicator) (‘reign’ = ‘rain’ = -RAIN-) from The Tempest (-STORM) (BRAINSTORM) offering to hold a group discussion (BRAINSTORM),
14 Penny whistles (PIPES) for desserts (desserts/pies = PI-ES) with soft (soft/piano = -P) centre? (PIPES),
16 Uncovered (UNVEILED) starter of unsalted (starter of ‘Unsalted’ = U-) head of langoustine (head of ‘Langoustine’ =-L-) in endive (endive) salad (= anagram indicator) (endive = -NVEI-ED) (UNVEILED),
17 In Brazil (RIO-) first team’s (first ‘Teams’ = -T) jerseys, socks and shorts (GEAR) (RIOT GEAR) worn by The Boys in Blue in case the crowd mob them (RIOT GEAR),
19 Could be (= anagram indicator) aware (aware = EARWA-), mystery man (-X) (EARWAX) is causing trouble for The Hearing (EARWAX),
21 Instructions for cooking (RECIPE) price- (price) -fixing (= anagram indicator) (price = RECIP-) for energy (-E) (RECIPE),
23 Clare, for one (Clare Island = ISLE), consumed by tennis lesson (consumed by ‘tennIS LEsson’ = ISLE),
24 Read aloud (= homophone indicator) novel (‘book’ = ‘BUCK’) with male rabbit (BUCK).