Across:
8 Turns up (= reversal indicator), suits partner (‘suit and tie’ = tie = -E IT) to go on one’s own (solo) for the most part (o) (‘solo’ without ‘o’ = sol = LOS-) (LOSE IT) or snap (LOSE IT),
9 One of The Mandibles (LOWER JAW) let down (LOWER) by mouthy type (JAW) (LOWER JAW),
10 Take a beating (LOSE) coming up (= reversal indicator) in part of The Solent (in part of ‘thE SOLent = esol = LOSE),
11 Popular (IN) graduate (BA-) getting degree (-D) for fashion (SHAPE) (IN BAD SHAPE) is really suffering (IN BAD SHAPE),
12 Allow (allow = WALLO-) cook (= anagram indicator) to prepare starter (‘Prepare’ starter = -P) (WALLOP) in batter (WALLOP),
14 Suspend (HANG) sponsor (BACK) (HANG BACK) of Remain in the shadows (HANG BACK),
15 Sounds like (= homophone indicator) mistakes (faults) in the serving (faults in the tennis serving: ‘faults’ = ‘FALSE’) and charge (ACCUSATION) (FALSE ACCUSATION) challenged by the barman perhaps (FALSE ACCUSATION),
18 A major employer (army) fires them (MISSILES) for hitting targets at a demonstration? (MISSILES),
20 Close one’s eyes (NOD OFF) to gesture (NOD-) from old (O-) party (Fianna Fáil = -FF) (NOD OFF),
22 It’s too important to interfere with (SACROSANCT) whales (orcas) raised (= reversal indicator) (orcas = SACRO-) on the beach (sand) briefly (‘sand’ without ‘d’ = SAN-) close to Connecticut (-CT) (SACROSANCT),
24 Go here and there (ROAM) with video from road movie (‘video’ from ‘road movie’ = roam = ROAM),
25 Old police force (RUC = -CUR-) comes up (= reversal indicator) in crime (crime) question (= anagram indicator) (crime = MER-IC) (MERCURIC) – it’s like something out of Quicksilver (like quicksilver/mercury = MERCURIC),
26 Courses (TRACKS) in School (-S) after (= positional indicator) finishing 13 down (finishing ‘loses track’ = TRACK-) (TRACKS).
Down:
1 Marsh (marsh = BOG-) loses head (i) a wee bit (‘iota’ without ‘i’ = -OTA) (BOGOTA) in American capital (BOGOTA capital of Colombia),
2 Characters travelling around (= reversal indicator) in double decker? (in ‘doublE DECker’ = edec = CEDE) I’ll give you that! (CEDE),
3 The (the = ETH-) organisation (= anagram indicator) gets in touch with Number 10 (-IO-) secretary (-P-A) around one (-I-) (ETHIOPIA) country in Africa (ETHIOPIA),
4 Strike (strike/beat = CLUB) in Mace (mace/cosh = CLUB),
5 Resist leaving dessert wines (‘resist’ leaving ‘dessert wines’ = dewnes = SWEDEN) in the country (SWEDEN),
6 It’s not allowed (PROHIBITED) in bar (PROHIBIT-) with a fair amount of (half of) weed (half of ‘weED’ = -ED) (PROHIBITED),
7 First get (first ‘Get’ = G-) map (A to Z map = -AZ-) and prepare to travel (pack) shortly (k) (‘pack’ without ‘k’ = -PAC-) for starters of homemade oxtail (starters of ‘Homemade Oxtail’ = -HO) (GAZPACHO) soup (GAZPACHO),
13 Comes a cropper (LOSES) on course (TRACK) (LOSES TRACK) as has failed to follow (LOSES TRACK),
14 One thousand (-K-) in used (= anagram indicator) cash (cash = HAC-S) (HACKS) for local journalists (HACKS),
16 Produced a type of film (ANIMATED) clip (l) of Bambi (‘animal’ without ‘l’ = ANIMA-) with the (the) heartless (h) (‘the’ without ‘h’ = -TE-) director (-D) (ANIMATED),
17 Tiny cast (tiny cast = SANCTITY) adapted (= anagram indicator) show of godliness (SANCTITY),
19 Opens 8 across (opens ‘lose it’ = LOSE-) to empty (d) RDS (‘RDS’ without ‘d’ = -RS) (LOSERS) of the total failures (LOSERS),
21 Pilot (fly) endlessly (y) (‘fly’ without ‘y’ = FL-) solicits (-ASKS) (FLASKS) those holding the drinks (FLASKS),
23 Score (NICK) central to revolutionary (= reversal indicator) landmark cinema (‘landmarK CINema’ = kcin = NICK),
24 Crept off red carpet (‘crept’ off ‘red carpet’ = reda = READ) in study (READ).