Across:
8 At the end of 15 across (‘leaves in no doubt’ = DOUBT-), society (-S) (DOUBTS) calls it into question (DOUBTS it),
9 Refuse to change one’s opinions of Americans (US stick to one’s opinion = STANDPAT) in part of the stadium (STAND-) going to clap (-PAT) (STANDPAT),
10 We had it all from the border’s (‘we had it all’ from the borders = WELL) spring (WELL),
11 A (A-) shrewd (-POLITIC-) gangster (-AL Capone) (APOLITICAL) with no interest in affairs of state (APOLITICAL),
12 Small (S-) place (-P-L) over crude (-RAW-) (SPRAWL) lounge (SPRAWL),
14 Is this Plan B designed to keep the border open politically (BACKSTOP) or to champion (BACK-) leaders supporting Tories opposing PM? (leaders “supporting Tories opposing PM” = -STOP) (BACKSTOP),
15 Checks out (LEAVES) hostelry (inn = IN N-) near Oxford (= -O) – reservation (DOUBT) (LEAVES IN NO DOUBT) means there’s no room for any confusion (LEAVES IN NO DOUBT),
18 Works (OPERATES) unresolved case (open case) brief (n) (‘open’ without ‘n’ = OPE-) for judges (-RATES) (OPERATES),
20 Tune in to (LISTEN) silent (silent = LISTEN) production (= anagram indicator),
22 No celibate (no celibate = NOTICEABLE) doctor (= anagram indicator) is to be seen (NOTICEABLE),
24 Large town (CITY) on the outskirts of civil engineering university (on the outskirts of ‘civil engineering university’ = CITY),
25 Quoted again (REPEATED) for a type of moss (-PEAT- moss) found in grass (RE-ED) (REPEATED),
26 Bookish types (LEAVES) opening 15 across (‘leaves in no doubt’ = LEAVES).
Down:
1 She leaves penthouse (‘she’ leaves ‘penthouse’ = pentou = TONE UP) for exercise (TONE UP),
2 First victim (ABEL) in list from the Bastille (‘list’ from the ‘Bastille’ = bale = ABEL),
3 Fool (ASS-) from Australia (-AU-) starts listening to strikers (starts ‘listening to strikers’ = -LTS) (ASSAULTS) from a number of clubs (clubs/beats = ASSAULTS),
4 Sample of mementos located (sample of ‘mementos located’ = OSLO) in capital (OSLO = capital of Norway),
5 Relative (MA-) is the first murderer (Cain = -NIAC) making a comeback (= reversal indicator) (MANIAC) in Psycho (MANIAC),
6 Claims (ADMISSIONS) these were heard in confessions (ADMISSIONS),
7 Lost (= anagram indicator) coat (coat = TACO-) and money (-M-) in taxi (CA-B) (CATACOMB) or The Underground tunnel, of late (CATACOMB),
13 It’s short (t) notice (‘advert’ without ‘t’ = ADVER-) to take exam again (resit = -TISER) turning up (= reversal indicator) (ADVERTISER) for job in promotions (ADVERTISER),
14 Safe places perhaps (BANKS) on both sides of The Liffey, for example (BANKS of river),
16 Goes off (EXPLODES) with former partner (EX-) to opening of play (opening of ‘play’ = -P-) with loads (‘loads’ = ‘lodes’ = -LODES) off the radio? (= homophone indicator) (EXPLODES),
17 Rocky (= anagram indicator) Lowell is (Lowell is = OIL WELLS) tapping into natural energy (OIL WELLS),
19 Posts: (TWEETS) “I ran away from wine taster” (‘I ran’ away from ‘wine taster’ = wetste = TWEETS),
21 Of course (ENTRéE course), this should get the juices flowing! (starter course = ENTRéE),
23 Dubs (dubs = BUDS) playing (= anagram indicator) with those who might bloom in the future (BUDS),
24 Pub (bar = - RAB) chain to open (‘chain’ to open = C-) up (= reversal indicator) (CRAB) – is that a sign? (CRAB is sign of Cancer).