Across:
8 Local mug (local 'mug' = rob) served up (= reversal indicator) (rob = BOR-) with endless (end 'lesS' = -S-) cold (-C-) and hot (-H) (BORSCH) soup? (BORSCH),
9 First Lady (-EVE-) falling into rocking (= anagram indicator) chair (chair = ACHI-R) (ACHIEVER) is the subject of a successful story (ACHIEVER),
10 Tiny parasites (LICE) in the public eye (in the ‘pubLIC Eye’ = LICE),
11 Mobiles (TELEPHONES) opening on 15 across (opening on ‘telephone number’ = TELEPHONE-) and ultimate campsites (ultimate ‘campsiteS’ = -S) (TELEPHONES),
12 Maintain pace with (KEEP UP) ambitious (keen) short (n) (‘keen’ without ‘n’ = KEE-) boxer (pup = -P UP) (KEEP UP),
14 Loud music (forte = F-) from a foreign (‘a’ foreign/French = -UNE-) capital (-REAL capital/currency of Brazil) (FUNEREAL) is not lively (FUNEREAL),
15 Ring (TELEPHONE) is one example (NUMBER) (TELEPHONE NUMBER) of the sort kept in a cell in America (TELEPHONE NUMBER kept in a cell/phone in America),
18 Evade his (evade his) problem (= anagram indicator) (evade his = ADHESIVE) – if you walk into it, you’ll find it hard to extricate yourself from it (ADHESIVE),
20 Julius Caesar got rid of juries (‘Julius Caesar’ got rid of/without ‘juries’ = luscaa = CASUAL) – how blasé is that? (CASUAL),
22 A nutritious, healthy dinner, for example (GOOD FOR YOU), well done! (GOOD FOR YOU),
24 Accommodates the brother (CELL in the abbey for the monk) in intellectual set-up (reverse indicator) (in ‘inteLLECtual’ = llec = CELL),
25 Organisation (United Nations = UN-) making a mistake (-ERRING) (UNERRING) for sure (UNERRING),
26 Characters at the end of 15 across (characters at the end of ‘telephone number’ = NUMBER) in 1984? (1,984 = NUMBER).
Down:
1 Is free to shift (MOBILE) something similar in 15 across, for starters (MOBILE is similar to starters of 'telephone number),
2 Clare, for one (Clare Island = ISLE), immersed in tennis lesson (immersed in ‘tennIS LEsson’ = ISLE),
3 Shelter (-HUT-) in Czech Republic (C-Z-) by chance (chance/luck = hap) set up (= reversal indicator) (hap = -PAH) (CHUTZPAH) by audacious, shameless type (CHUTZPAH),
4 Caught up (= reverse indicator) in manual labour (caught up in ‘manuaL LABour’ = llab = BALL)? It awaits Cinderella! (BALL),
5 The writer of the music (Frédéric CHOPIN) from One (-I-) Direction (North = -N) behind (= position indicator) split (CHOP-) (CHOPIN),
6 Adore (adore) showing off (= anagram indicator) (adore = AEROD-) European capital (Rome = -ROME-) society (-S) (AERODROMES) from the homes of the high flyers (AERODROMES),
7 Large jug (-EWER-) carried by wise guy (sage = S-AGE) (SEWERAGE) in America going to waste (SEWERAGE is the American spelling of sewage),
13 They’re putting on an act (PRETENDERS) with slippery (= anagram indicator) red serpent (red serpent = PRETENDERS),
14 Cross Swords (cross swords in fencing = FENCE) by going around the border (FENCE goes around border of property, for instance),
16 The A-Z, for example (END TO END), for all those involved in a row? (END TO END),
17 Composition (NOCTURNE) is not (not) endless (t) (‘not’ without ‘t’ = NO-) about revolution (-TURN-) in church (Church of England = C-E) (NOCTURNE)
19 One (I-) company (-CO-) not the first (‘Not’ the first = -N-) in charge of (-IC) (ICONIC) of a sacred image (ICONIC),
21 Snake (asp = AS-P) found around river (River -LEE-) (ASLEEP) is dead to the world (ASLEEP),
23 Agony aunt’s losing suntan (‘agony aunts’ losing ‘suntan’ = goya = YOGA) in exercise that comes with discipline (YOGA),
24 Group (group/side = CAMP) cut initially (‘Cut’ initially = C-) from Band Aid (band aid is an -AMP) (CAMP).