Across:
8 Unnerve someone (RATTLE) on the ramparts of Rathangan Castle (on the ramparts of ‘RAThangan CasTLE’ = RATTLE),
9 Went one better than (EXCEEDED) divorcee (EX-) from old community (EEC) retiring (= reversal indicator) (EEC = -CEE-) to Germany (Germany domain = de. = -DE-) on Dutch border (‘Dutch’ border = -D) (EXCEEDED),
10 Throws light on alley (LAMP), as characters in in Strip Mall (characters in ‘striP MALl’ = pmal) are back (= reversal indicator) (pmal = LAMP),
11 Frank (OPEN -) is looked after (-MINDED) (OPEN-MINDED) by liberal (OPEN-MINDED),
12 What one of those in Labour (work) has to show for a lifetime (CAREER) in Rush? (rush/dash = CAREER),
14 Talking Heads (PANEL) and Spike (PIN) (PANEL PIN) presumably getting hammered (PANEL PIN),
15 Katy did (katydid = INSECT) horrible thing (REPELLENT) (INSECT REPELLENT) – it causes them to drop like flies perhaps (INSECT REPELLENT),
18 Sporting lady paid out (‘sporting lady’ without ‘paid’ = sortngly = STRONGLY) solidly (STRONGLY),
20 Cultured (URBANE) city (URBAN-) at the end of Caliphate (at the end of ‘CaliphatE’ =-E) (URBANE),
22 Successful (VICTORIOUS) man (VICTOR-) loses the head (p) with God-fearing type (‘pious’ without ‘p’ = -IOUS) (VICTORIOUS),
24 Study (ROOM) by one of those in The House (ROOM),
25 Popular (IN-) writer (-SCRIBE) (INSCRIBE) of score (score/etch = INSCRIBE),
26 Know all (know-all = ORACLE) the old (O-) Irish people, for instance (race = -RAC-E), around Limerick (-L-) (ORACLE).
Down:
1 Megalomaniac releases income (‘megalomaniac’ releases ‘income’ = mgalaa = MALAGA) from Iberian port (MALAGA),
2 Jack in (pack in/quit = STOP) part of Sevastopol (part of ‘sevaSTOPol’ = STOP),
3 Protest (DEMO-) at college (-C-) backed (= reversal indicator) pitch (tar = -RAT-) (DEMOCRAT) by one committed to the house party (DEMOCRAT),
4 Goes around getting the job done (goes around ‘GEtting the job doNE’ = GENE) – it’s a character builder (GENE),
5 It’s not in mint sauce (‘its’ not in ‘mint sauce’ = mnauce = ACUMEN) – that much is common sense (ACUMEN),
6 Looks after the boxers, among others (KENNEL CLUB), in the doghouse (KENNEL) for going dancing (CLUB) (KENNEL CLUB),
7 Ned Eliot (Ned Eliot) played (= anagram indicator) (Ned Eliot = DELETION) with Erasure (DELETION),
13 It’s capable of bringing the viewers together (EYE CONTACT) to spy (EYE) on informer (CONTACT) (EYE CONTACT),
14 Egyptians sang out (‘Egyptians’ sang out/without ‘sang’ = eypti = PIETY) with a sense of religious reverence (PIETY),
16 Nutter in (nutter in) trouble (= anagram indicator) (nutter in = NUTRIENT) providing a source of nourishment (NUTRIENT),
17 Is removed from limousine’s (‘is’ removed from ‘limousines’ = lmouines = EMULSION) watery type of paintwork (EMULSION),
19 Fishy type (GAR-) of starters with lobsters in ceviche (starters with ‘Lobsters In Ceviche’ = -LIC) (GARLIC) that leaves a pungent aroma on the breath (GARLIC),
21 Old one (old one) suspects (= anagram indicator) (old one = NOODLE) the local fool (NOODLE),
23 A jar (ajar = OPEN) with old (O-) writer? (-PEN) (OPEN),
24 Non-fictional (REAL) rebellious (= reversal indicator) characters from Thermopylae remembered (characters from ‘ThermopyLAE Remembered’ = laer = REAL).