Across:
1 Provoke (INCITE) dietician to release aid (‘dietician’ to release ‘aid’ = ieticn = INCITE)
4 Spreads bits about (SCATTERS) models (= anagram indicator), stars, etc. (stars etc = SCATTERS),
9 What was the function (SOCIAL) of The Gathering? (SOCIAL),
10 By the sounds of it, you might have heard this from 25 across (SYMPHONY from ‘stereo’) or in Mozart’s Prague? (Mozart’s Prague Symphony No 38 = SYMPHONY),
12 Is not going to be walked all over (RESILIENT) playing (= anagram indicator) Leinster (Leinster = RESIL-ENT) holding onto lead at interval (lead at ‘Interval’ = -I-) (RESILIENT),
13 Rebellious (= reverse indicator) segment of Jeunesse dorée (segment of ‘jeuNESSE dorée’ = nesse = ESSEN) found in Germany (ESSEN),
14 One there for the taking (BURGLAR) raises red flag? (ALARM) (BURGLAR ALARM) You often hear that in relation to unwelcome visitors! (BURGLAR ALARM),
18 Working overseas (MERCHANT NAVY) with dealer (MERCHANT) – a dark, colourful type (NAVY) – (MERCHANT NAVY),
21 Some emperor regards (some ‘empeROR REgards’ = rorre) Rising (= reverse indicator) (rorre = ERROR) as a mistake (ERROR),
22 Swinging (= anagram indicator) gorilla (gorilla = ALLIG-OR) grabs a (-A-) serpent’s tail (serpent’s tail/tail of ‘serpenT’ = -T-) (ALLIGATOR) hiding in swampland (ALLIGATOR),
24 Sounds of young people (POP MUSIC) encouraging Dad dancing presumably? (unfashionable “dad dancing” to POP MUSIC),
25 Colour sergeant ignores clangour (‘colour sergeant’ ignores ‘clangour’ = oseret = STEREO) from music system (STEREO),
26 It’s not easy (it’s hard = H-ARD-) welcoming order (-O-) in (-IN-) Government (-G) (HOARDING) that amounts to regular savings (HOARDING),
27 Dawn coming out of swamplands (‘Dawn’ coming out of ‘swamplands’ = sampls = PSALMS) often recalled by father from good books (PSALMS).
Down:
1 Popular (IN-) writer (-SCRIBE) (INSCRIBE) of score (score/etch = INSCRIBE),
2 Cold (C-) salad (= anagram indicator) course (course = -OC-SURE) over the weekend (‘weeK’ end = -K-) (COCKSURE) produced in an arrogantly confident way (COCKSURE),
3 Lose (-L) after (= position indicator) endless (n) exercise (train) (‘train’ without ‘n’ = TRAI-) (TRAIL) and find oneself behind the others (TRAIL),
5 Those with global visions (CRYSTAL BALLS) employed by those looking into the future for advance information (CRYSTAL BALLS),
6 What’s highly classified? (TOP SECRET) God knows! (TOP SECRET),
7 It goes (it goes) badly (= anagram indicator) (it goes = EGOIST) for promoter of the selfie perhaps? (EGOIST),
8 Having a look behind the curtain (snooping = SPYING) – that’s a job for the agency (job for CIA agency / SPYING),
11 It never goes up (DEPRECIATION) in financial crash (DEPRECIATION),
15 Relax (LIE AROUND) with a (A-) few drinks from the bar (-ROUND) after (= positional indicator) a whopper (LIE) (LIE AROUND),
16 Patrols (patrols = PASTOR-L) all over the place (= anagram indicator) around American border (‘American’ border = -A-) (PASTORAL) in rural area (PASTORAL),
17 Cunning, youthful protester starts (‘Cunning Youthful Protester’ starts = CYP-) disturbances (-RIOTS) (CYPRIOTS) with Mediterranean islanders (CYPRIOTS),
19 Prometheus dismissed sour (‘Prometheus’ dismissed ‘sour’ = pmethe = TEMPEH) dish made with fermented soya (TEMPEH)
20 The Gaelic players’ Rep (Gaelic Players Association = GPA = G-PA) accepts rebuke (-RAP-) (GRAPPA) for one drunk in Italy (GRAPPA),
23 Openings (GATES) for one from Stone Age (‘one’ from ‘Stone Age’ = stage = GATES).