Across:
8 Charlie (C-) Buck (dollar) needs no introduction (d) ('dollar' without 'd' = -OLLAR) (COLLAR) to Van Dyke, for one (Van Dyke is a COLLAR),
9 Proof (EVIDENCE) from Germany (Germany domain = .de = -DE-) divides Venice? (Venice) Wrong! (= anagram indicator) (Venice = EVI-NCE) (EVIDENCE),
10 Barge from Bronze Age (‘barge’ from ‘bronze age = onze = ZONE) produced in a particular area (ZONE),
11 The poor beggars (MENDICANTS) administering to the sick in a hospital (medic = ME-DIC-) getting to grips with new (-N-) workers (-ANTS) (MENDICANTS),
12 A lot fell off alternator (‘a lot’ fell off ‘alternator’ = ternar = ERRANT) and it’s not in the right place of course (ERRANT),
14 Found at the start of 15 across (at the start of ‘collect evidence’ = COLLECT-)? School (-S) (COLLECTS) clusters! (COLLECTS),
15 Pick up (COLLECT) characters in 9 across (characters in ‘evidence’ = EVIDENCE) for work, in a way, that might require conviction in the end? (COLLECT EVIDENCE),
18 Gave up the ghost (died = DI-ED) over article (-THE-) – writing (from the 3Rs = -R-) (DITHERED) was indecisive (DITHERED),
20 Refused to endorse (VETOED) one of those checking out great Dane (dog) (VET-) around (-O-) Elsinore primarily (‘Elsinore’ primarily = -E-) and that’s key (music key -D) (VETOED),
22 Starters of veal in batter (starters of ‘Veal In Batter’ = VIB-) – portion (-RATION-) with side salad (side ‘Salad’ = -S) (VIBRATIONS) and shakes (VIBRATIONS),
24 Cable (WIRE) going around winter tyre (going around ‘WInter tyRE’ = WIRE),
25 The guard (the guard) running riot (= anagram indicator) (the guard = DAUGHTER) in the family (DAUGHTER),
26 Treasury (coffers) loses capital (c) (‘coffers’ without ‘c’ = OFFERS) reserves (OFFERS).
Down:
1 Celtic is not in technicolour ('celtic' is not in 'technicolour' = hnoour = HONOUR) – there's no shame in that! (HONOUR),
2 Pupil (learner = -L-) from youth centre (‘yoUth’ centre = -U-) in Clare (CE = C-E) (CLUE) is sought by detective (CLUE),
3 Ita (Ita = -ATI-) More (more) – is not finished (e) (‘more’ without ‘e’ = mor = -ROM-) in California (CA = A-C) raising all (= reverse all indicator) (AROMATIC) the roses in the fragrant sense (AROMATIC),
4 Mean partner (mean and LEAN) of Al Capone gets rid of Capo (‘Al Capone’ gets rid of ‘Capo’ = alne = LEAN),
5 Describing a relative issue (FILIAL), one of those in The Cabinet (file) reduced (e) (‘file’ without ‘e’ = FIL-) Unit (-I-) at Health Centre (‘heALth’ centre = -AL) (FILIAL),
6 Degradation (DEBASEMENT) of foreign (= anagram indicator) sea (sea = -ASE-) workers (-MEN-) found in arrears (debt = DEB-T) (DEBASEMENT),
7 Turns up (= reverse indicator), church (Church of England = CE = EC-) is not likely to be moved (-STATIC) (ECSTATIC) by seventh heaven? (ECSTATIC),
13 Every ounce of anger (ALL THE RAGE) in Vogue (in vogue = ALL THE RAGE),
14 Charlie (C-) and Fawn’s group (deer) going backwards (= reverse indicator) (deer = -REED) (CREED) in Tenet? (CREED),
16 The first (ORIGINAL) Generalissimo seems out of it? (‘Generalissimo’ seems out of it/without ‘seems’ = gnraliio = ORIGINAL),
17 Produced (= anagram indicator) VISA (Visa = -VASI-) for order (-O-) in public house (inn = IN-N) (INVASION) by stream over the border? (INVASION),
19 Bake (= anagram indicator) a torte (a torte = ROTATE) to go around (ROTATE),
21 Mistakes (ERRORS) produced by those characters in the USSR or Republic (in ‘the usSR OR REpublic’ = srorre) going all the way back (= reversal indicator) (srorre = ERRORS)
23 Gets high (soars), loses head (s) (‘soars’ without ‘s’ = OARS) and rows (OARS),
24 Partner (WIFE) of fellow at foundation (‘felloW’ at foundation = W-) provided (-IF-) initial evidence (initial ‘Evidence’ = -E) (WIFE).