Across:
8 Poison from mountaintop’s (‘poison’ from ‘mountaintops’ = mutant = MUTANT) freak of nature (MUTANT),
9 Hooligan (TEARAWAY) from Split (split/rip = TEAR-) is on holiday (-AWAY) (TEARAWAY),
10 Pay no attention to (PASS) separatist with no attire (‘separatist’ with no ‘attire’ = spas = PASS).
11 Nuisance (pest = P-EST) admits a (-A-) lack of energy (-LIMP-) at school (-S) (PALIMPSEST) producing reused manuscript (PALIMPSEST),
12 Burned (burned) out (= anagram indicator) (burned = BURDEN) by the responsibility one has to carry (BURDEN),
14 Ignores a (ignores a) rogue (= anagram indicator) (ignores a = ORGANISE) group (ORGANISE),
15 Ask for money (PASS THE HAT ROUND) from 10 across (‘pass’ = PASS) for article in 14 down (article/definite article in ‘other’ = THE) joining most of 24 down (most of ‘hats’ = HAT) and most of 21 down (most of ‘around’ = ROUND) (PASS THE HAT ROUND),
18 Party (CAROUSE-) leader, the last (‘leadeR’ the last = -R) (CAROUSER) type you’d expect to go on the tear (CAROUSER),
20 One of those in Dublin Airport (Terminal 1 = T1) is a double (T1 x 2 = TITI-) for an (-AN) (TITIAN) artist from the Venetian school (TITIAN)
22 Half of 25 across (half of ‘PASSport’ = PASS) from Irish province (Munster) losing direction (north = ‘n’) (‘munster’ without ‘n’ = MUSTER) (PASS MUSTER) come up to scratch (PASS MUSTER),
24 Local belt (local ‘belt’ = HOOK) taken by boxer perhaps (HOOK),
25 Free admission (PASS-) to harbour (-PORT) (PASSPORT) for one going overseas (PASSPORT),
26 Recording (NOTING) away (not in = NOTIN-) game from the start (‘Game’ from the start = -G) (NOTING).
Down:
1 End product (end ‘producT’ = T-) is superior (upper-class = -U-) and provides endless (e) value (‘value’ without ‘e’ = -VALU) (TUVALU) for what is now the Ellice Islands (the Ellice Islands are now TUVALU),
2 France is out of fragrances (‘France’ is out of ‘fragrances’ = gras = RAGS) and cloths for cleaning (RAGS),
3 A (A-) regular fixture in the pub (tap = -T A P-) – a small measure (-INCH) (AT A PINCH) but only if absolutely necessary! (AT A PINCH),
4 Back (= reversal indicator) running behind (late = ET AL) the others in old Rome (ET AL),
5 The foreign (the = LA-) director general (director general = -D -G) catches relative (MA-) (LAD MAG) with playboy (Playboy magazine = LAD MAG),
6 Opening 22 across (opening ‘pass muster’ = PASS) popular (-IN-) with The Force? (-G force) It’s common knowledge (OUT) (PASSING OUT) it’s what graduates from Templemore are doing! (PASSING OUT),
7 Chooses not to accept (PASSES ON) 10 across (‘pass’ = PASS-) from English (-E-) relative (son = -S ON) (PASSES ON),
13 Deprive (DISPOSSESS) detectives (DIs = DIS-) and sheriffs’ men (-POSSES-) at the start of spree (at the start of ‘Spree’ = -S) (DISPOSSESS),
14 What’s the alternative (OTHER) to relative (mother) losing the head? (m) (‘mother’ without ‘m’ = OTHER),
16 Reviews (= reversal indicator) Indian music (raga = agar) a couple of times (agar x 2 = AGAR-AGAR), as it’s a cultural phenomenon at The Strand (in seaweed / biological culture = AGAR-AGAR),
17 Working in place of Dean (Dean in university / TUTORING) teaching others a lesson (TUTORING),
19 Proust (Proust) drunk (= anagram indicator) (Proust = STUPOR) to the state of unconsciousness (STUPOR),
21 Roughly (AROUND) what you might acquire at the 19th hole (get ‘a round’ in golf clubhouse/bar = AROUND),
23 Caught up (= reversal indicator) in Aristotelian (in ‘ariSTOTelian’ = stot = TOTS) nursery group (TOTS).
24 Panama’s (Panamas = HATS) coast – a holiday in itself (‘coaST A Holiday’ in itself = stah) looking back (= reversal indicator) (stah = HATS).