Across:
8 Detective (-PI-) in Mayo (Mayo) confused (= anagram indicator) (Mayo = MYO-A) (MYOPIA) by lack of imagination (lack of imagination/foresight = MYOPIA),
9 Like The Goth’s (GERMANIC people) description of 3 down, for example (GERMANIC is a description of ‘Bavarian’),
10 A jar (ajar = OPEN) with old (O-) writer? (-PEN) (OPEN),
11 Some people will lose sleep over this (ALARM CLOCK), with grandfather possibly providing a wake-up call for others (grandfather clock perhaps = ALARM CLOCK),
12 Month (OCT-) before (= positional indicator) Ireland (Republic of Ireland = -ROI) (OCTROI) could use this to raise old tax (OCTROI),
14 Hooligan (TEARAWAY) from Split (TEAR-) is on holiday (-AWAY) (TEARAWAY),
15 Dogs (pursues = dogs = GERMAN SHEPHERDS) 21 down (‘German’ = GERMAN) and those figures associated with crooks? (crooks/hooked staffs for SHEPHERDS) (GERMAN SHEPHERDS)
18 Give it one’s best shot (STRUGGLE) with horse (-GG-) in Ulster (Ulster = STRU-LE) run (= anagram indicator) (STRUGGLE),
20 Heartless (heartless = remove centre = ‘r’) act of violence (‘outrage’ without ‘r’ = OUTAGE) symptomatic with a loss of power (OUTAGE),
22 Drunk in the Mosel (GERMAN WINE) in 21 down (‘German” = GERMAN) and in 24 down (‘wine’ = WINE) (GERMAN WINE),
24 It’s for fighting (WAR-) delirium initially (‘Delirium’ initially = -D) (WARD) in hospital (WARD),
25 The man will (he will = he’ll = HELL-) get out of shape (-BENT) (HELL-BENT) in tent? (intent = HELL-BENT),
26 Say it isn’t so (DENIAL), as it wasn’t me (DENIAL).
Down:
1 Relates to what’s in 8 across (MYOPIC relates to ‘myopia’) or in my (MY-) old (-O-) photograph (-PIC) (MYOPIC),
2 Quick trip (SPIN) around the Spanish Main (around the ‘SPanish maIN’ = SPIN),
3 Sign (-V- sign) in Arabian (Arabian) train (= anagram indicator) (Arabian = BA-ARIAN) (BAVARIAN) is similar to one of those in 21 down (BAVARIAN is ‘German’),
4 Covered by Mario Vargas Llosa (covered by ‘mario vARGAs llosa’ = arga) back (= reversal indicator) (arga = AGRA) in Indian city (AGRA),
5 The police are looking into this (CRIME-) area (-A) (CRIMEA) and region in the Black Sea peninsula (CRIMEA),
6 Father (parent = PAR-ENT) admits taking post (mail) up (= reversal indicator) (mail = -LIAM-) (PARLIAMENT) in the house (PARLIAMENT),
7 Pressure (P-) on one (-I-) taking exam (Leaving Cert = -LC-) is not easy (is -HARD) (PILCHARD) for one of those in school (PILCHARD in school of fish),
13 The dogs in the street are aware of this (RUMOUR MILL) producer of fictional works perhaps (RUMOUR MILL),
14 See the light dismissing slight (‘see the light’ dismissing ‘slight’ = eethe = TE-HEE) little laugh (TE-HEE variant of ‘tee-hee’),
16 The highs and lows (EXTREMES) of former (EX-) lead musician (lead ‘Musician’ = -M-) in The Hollies, for example (trees = -TRE-ES) (EXTREMES),
17 Paid man in Ring perhaps (boxer = professional = PRO-) with Clare (-CE-) writer’s (-EDS) (PROCEEDS) royalties (PROCEEDS)
19 Hang glider drops dahl (‘hang glider’ drops ‘dahl’ = nggier = GINGER) with hot aromatic spice (GINGER),
21 Frenchman (Monsieur = -M-) in Range (range) Rover (= anagram indicator) (range = GER-AN) (GERMAN), in a manner of speaking on the Continent (GERMAN),
23 Very small amount (IOTA) amidst audiotapes (amidst ‘audIOTApes’ = IOTA),
24 Held leaving New Delhi (‘held’ leaving ‘New Delhi’ = newi = WINE) port (WINE).