Across:
8 There used to be one of these in 23 down (SOVIET in ‘USSR’) for revolutionary council (SOVIET),
9 Kneels (kneels = SKELE-N) excited (= anagram indicator) over bone (-T- bone) from duck (-O-) (SKELETON) found in archaeological site (SKELETON),
10 Leave it out (OMIT), as it’s got nothing (O-) to do with short (e) prison sentence (time) being raised? (= reversal indicator) (‘time’ = ‘emit’ = without ‘e’ = -MIT) (OMIT),
11 It’s similar to one of those in 21 down (one ‘rider’ is similar to ADDITION-) with a (-A-) line (-L) (ADDITIONAL) that’s extra (ADDITIONAL),
12 Press (press/cupboard = CLOSET) club (C-) can’t be found (-LOS-T) going around Spain (-E-) (CLOSET),
14 Upsets (= reversal indicator) old (-O) staff (rod = -DOR-) in Dell (dell = dale = EL -AD-) (EL DORADO) famous for supplying precious material from Amazon (EL DORADO),
15 Player’s (players = ACTORS) backbone (CHARACTER) opened (= positional indicator) (CHARACTER ACTORS) by those in the theatre, not the main ones (CHARACTER ACTORS),
18 No more (no more = ENORMO-) soup (= anagram indicator) for you and me (-US) (ENORMOUS) – it’s mighty! (ENORMOUS),
20 Be on the safe side (SECURE) with breakdown (= anagram indicator) rescue (rescue = SECURE),
22 Replacement (SUBSTITUTE) comes from butchers (= anagram indicator) but it’s suet! (but its suet = SUBSTITUTE),
24 Relatives (DADS) locked up by Trinidad security (locked up by ‘Trinidad security’ = DADS),
25 Gatherings (REUNIONS) of neurons (neurons = REUN-ONS) travelling (= anagram indicator) around centre of spine (centre of ‘spine’ = -I-) (REUNIONS),
26 Complete (ENTIRE) building (= anagram indicator) in tree (in tree = ENTIRE).
Down:
1 It’s commonplace (NORMAL) to roam (roam = -ORMA-) freely (= anagram indicator) in The Netherlands (N-L) (NORMAL),
2 Some of the belief is traditional (some of the ‘belief is traditional’ = FIST) and that can hurt when hit with it (FIST),
3 Unfinished (a) American city (‘Atlanta’ without ‘a’ = ATLANT-) opens in chaos (opens ‘in chaos’ = IC) (ATLANTIC) and it divides Europe and the New World (ATLANTIC),
4 Stopped to think (mused), scratched the head (m) (‘mused’ without ‘m’ = USED), and applied it (USED),
5 Melanie (MEL-) and Edward (-TED) (MELTED) Thaw, from the past (past tense of thaw = thawed = MELTED),
6 Funny (= anagram indicator) comedic art (comedic art = DEMOCRATIC) is systematic of a structure of government (DEMOCRATIC),
7 Firm (CO-) ground (-LAND-) is fairly (half of) level (half of ‘tier’ = -ER) (COLANDER) and, being porous, is incapable of holding water (COLANDER),
13 Nearly (e) certain (‘sure’ = SUR-) initial planning (initial ‘planning’ = -P-) for Easter 1916 (-RISING) (SURPRISING) not predictable (SURPRISING),
14 What’s the chances (EVENS) of veterans getting rid of rat? (‘veterans’ getting rid of ‘rat’ = veens = EVENS),
16 Perfect (perfect/refine = hone) for the most part (e) (‘hone’ without ‘e’ = HON-) in Paris where (Paris/French ‘where’ = -OU-) revolutionary (-RED) (HONOURED) is held in high esteem (HONOURED),
17 Reads new (reads new = ANSWERED) amendment (= anagram indicator) with rebutted response (ANSWERED),
19 Turns up (= reversal indicator) no (no = -ON) teacher (Sir = -RIS-) is ordered to start (‘ordered’ to start = O-) (ORISON) prayer (ORISON),
21 Qualifications (RIDERS) for those working on The Curragh (RIDERS),
23 Russians dismiss a sin (‘Russians’ dismiss ‘a sin’ = russ = USSR) by old European empire, initially (USSR),
24 Some recommend a takeover (some ‘recommend a takeover’ = DATA) that’s important on fact-finding mission (DATA).