Across:
8 The end of the line (BURIAL) for British (B-) wild sheep (-URIAL sheep) (BURIAL),
9 Recalls (= reverse indicator) Russell (George William Russell = AE Russell = AE = EA-) Argyle (Argyle) working (= anagram indicator) (Argyle = -GLE RAY) (EAGLE RAY) in school (EAGLE RAY),
10 The Castle (FORT) limits, for the most part (limits ‘FOr the most paRT’ = FORT),
11 Minister (Rev) retires (= reverse indicator) (Rev = VER-) a better (a better) boss (= anagram indicator) (a better = -TEBRATE) (VERTEBRATE) or a beastly type with backbone? (VERTEBRATE),
12 Iranian neighbour (AFGHAN) provides a (A-) party (Fine Gael = -FG-) for Chinese ethnic group (-HAN) (AFGHAN),
14 It’s rigged (MAST-) by old (-O-) gangster (-DON) (MASTODON) from what looks like an old jumbo (MASTODON is extinct elephant-like creature),
15 Substandard (POOR) worker (HAND-) gets text (-WRITING) (POOR HANDWRITING), that’s hard to read (POOR HANDWRITING),
18 One (I-) atlas in (atlas in) production (= anagram indicator) (atlas in = -TALIANS) (ITALIANS) for the Austrian neighbours (ITALIANS),
20 Organisation (UN-) sounds like (= homophone indicator) it’s on drugs (‘Es’ = ‘ease’ = -EASE) (UNEASE) – it’s a cause for anxiety (UNEASE),
22 Enormous (GIANT) park (P-) not to mention (-AND-) area (-A) (GIANT PANDA) for endangered species (GIANT PANDA),
24 Part of revolutionary (= reverse indicator) pamphlet – a metaphysical (part of ‘pamphlET A Metaphysical’ = etam = MATE) type that’s one of a pair (MATE),
25 Musical talent (-EAR-) behind (= positional indicator) loud music (forte = F-) at takeaway (-LESS) (FEARLESS) is not afraid to have a go (FEARLESS),
26 Gathers away from ghetto blaster (‘gathers’ away from ‘ghetto blaster’ = ttoble = BOTTLE) with one of those full of drink (BOTTLE).
Down:
1 Clip (CUT OFF) of Partition (CUT OFF),
2 Part of the problem in trusting (part of the ‘probleM IN Trusting’ = MINT) one of those making their own dough (MINT making dough/money),
3 Elvis on a (Elvis on a) tour (= anagram indicator) (Elvis on a = SLOVENIA) in European country (SLOVENIA),
4 Bitter (BEER) with believer dismissing evil (‘believer’ dismissing ‘evil’ = beer = BEER),
5 A (A-) part of the golf course (green) cut short (n) (‘green’ without ‘n’ = -GREE-) for society (-S) (AGREES) matches (AGREES),
6 One of those providing Dutch courage (BEER BOTTLE) for 4 down (‘beer’ = BEER) and 26 across (‘bottle’ = BOTTLE) (BEER BOTTLE),
7 Half of Bray (half of ‘hee-HAW’ = HAW-) going north (north) incredibly (= anagram indicator) (north = -THORN) (HAWTHORN) with relative of Rose? (the rose is in the same family of trees as the HAWTHORN),
13 Zealots (HARDLINERS) destroying (= anagram indicator) Ireland (Ireland = -ARDLINE-) in hours (hrs = H-RS) (HARDLINERS),
14 Posers (models) with no heart, quality (no heart of ‘quaLity’ = l) (‘models’ without ‘l’ = MODES) or manners (manners/ways = MODES),
16 Detour is (detour is) all over the place (= anagram indicator) (detour is = OUTSIDER) out of The Loop (OUTSIDER),
17 Champagne and German wine (both types of RHUBARBS)? They’re a bit stalky for dessert (RHUBARBS),
19 Makes fun of (AP-ES) hiding place (-PL-) inside (APPLES) for making cider (APPLES),
21 Give it time to rest (SETTLE), as there’s no acidity primarily (‘Acidity’ primarily = a) in Washington port (Seattle) (‘Seattle’ without ‘a’ = SETTLE),
23 One of those on the plane (NOSE) is picked up in Bordeaux (Bordeaux wine / NOSE),
24 Bit of gloomy thought (bit of ‘glooMY THought’ = MYTH) in allegory (MYTH).