Across:
8 Is rare (is rare = SIERRA) cuckoo (= anagram indicator) from a range of mountains?
(SIERRA),
9 Important Russians (CZARINAS) transformed (= anagram indicator) Nazi cars (Nazi cars = CZARINAS),
10 Speech therapist misses teacher’s pet (‘speech therapist’ misses ‘teachers pet’ = shpi = SHIP) in A View from The Bridge, perhaps (SHIP),
11 Finishes 15 across (‘golden handshake’ = HANDSHAKE-) with small (-S) (HANDSHAKES) welcoming gestures (HANDSHAKES),
12 Opens 15 across (‘golden handshake’ = GOLDEN) full of promise, in an opportunistic sense (GOLDEN opportunity),
14 Comes (COM-ES) across dog (-PET-) (COMPETES) that has a chance of winning (COMPETES),
15 Describes precious type (GOLDEN) in 24 across (‘hand’ = HAND-) and most of those in 26 across (most of ‘shakes’= -SHAKE) (GOLDEN HANDSHAKE) for those retiring types in Labour (GOLDEN HANDSHAKE for those retiring types in labour/work),
18 Most of (e) the score (score/mark = ‘line’ without ‘e’ = LIN-) by Chopin (Chopin) lacks order (o) (‘Chopin’ without ‘o’ = -CHPIN) (LINCHPIN) and that’s vital to the organisation (LINCHPIN / lynchpin),
20 Can leave champions (‘can’ leave ‘champions’ = hmpios = MOPISH) down in the dumps? (MOPISH),
22 Turns up (= reversal indicator), the foreign (the = la = -AL) army unit (corps) isn’t finished (s) (‘corps’ without ‘s’ = corp = -PROC-) getting diamonds (ice = -ECI-) at the end of the war (end of ‘war’ = R-) (RECIPROCAL) – and the feeling is mutual (RECIPROCAL),
24 No lets in Shetland (no ‘lets’ in ‘Shetland’ = hand = HAND) for worker (HAND),
25 Removed the bones from (FILLETED) accommodation (-LET-) in field (field = FIL-ED) trip (= anagram indicator) (FILLETED),
26 Arab leader’s (Arab leaders = “sheiks” = “SHAKES”) report (= homophone indicator) throws one off balance (SHAKES).
Down:
1 Just (RIGHT-) got nothing (-O) (RIGHTO) for The Confirmation (RIGHTO),
2 Shop girl has no hols (‘shop girl’ has no ‘hols’ = pgir = GRIP) to cling to (GRIP),
3 Take advantage of (CASH IN ON) criminal (C- ON) hiding a (-A-) bit of a beef (shin = -SH IN) (CASH IN ON),
4 Celebrity (ICON) is charged (I-ON) over cocaine (-C-) (ICON),
5 A liberating demand (RANSOM) from strange (= anagram indicator) Romans (Romans = RANSOM),
6 Detective (PI-) and judge (-RATE) from 10 across (‘ship’ = SHIP) (PIRATE SHIP) working overseas illegally (PIRATE SHIP),
7 Ask for local money (locally ‘tap’ someone for money = TAP-) from the English (-E) terrace (DECK) (TAPE DECK) – it’s an old system one hears about (TAPE DECK),
13 Takeaway (DEDUCT-) opens before lunch (opens ‘before lunch’ = -BL-) in Ireland (Ireland domain = .ie = -I-E) (DEDUCTIBLE) and the Revenue is having none of it (DEDUCTIBLE),
14 Is that an ongoing reaction (CHAIN reaction) in Red (= anagram indicator) China? (China = CHAIN),
16 Circle (O-) backs (= reversal indicator) diabolical (evil = -LIVE) crude type (OIL) (OLIVE OIL) coming from The Press in Greece (OLIVE OIL),
17 Finds (= anagram indicator) mole (mole = -EMOL-) is overseeing part of China (D-ISH) (DEMOLISH) to topple the obstruction (DEMOLISH),
19 Grace O’Malley (PIRATE) opens 6 down (‘pirate ship’ = PIRATE),
21 Nuns (nuns = SUN-N) travelling (= anagram indicator) around Kildare (-KE-) (SUNKEN) dropped in at the deep end perhaps (SUNKEN),
23 Set of standards (CODE) for banks countrywide (banks ‘countrywide’ = CODE),
24 Moth-eaten Monet is left out (‘moth-eaten’ Monet is left out/without ‘Monet’ = thea = HEAT) in the hot weather (HEAT).