Across:
8 Saddle someone with (IMPOSE) producing introduction to inherently (introduction to ‘Inherently’ = I-) bad (= anagram indicator) poems (poems = -MPOSE) (IMPOSE),
9 Did time in detention centre perhaps (EDUCATED) and learned a lesson (EDUCATED),
10 Take stock from tuck shops (take ‘stock’ from ‘tuck shops’ = uhps = PUSH) to promote (PUSH),
11 Masterminded (ENGINEERED) in Greene (Greene) novel (= anagram indicator) (Greene = ENG-EER) about popular (-IN-) writer (-ED) (ENGINEERED),
12 Ship factory has no craft (‘ship factory’ has no ‘craft’ = shipoy = PHYSIO) job for a hands-on type of person (PHYSIO),
14 Former partner (EX-) engineering (-E-) court (court) action (= anagram indicator) (court = -CUTOR) (EXECUTOR) – it’s to do with whether Will gave him a job? (EXECUTOR),
15 Blow a fuse (FLY OFF THE HANDLE) and lose it (FLY OFF THE HANDLE),
18 Breathes new life into (ANIMATES) mates in a (mates in a) production (= anagram indicator) (mates in a = ANIMATES),
20 Slow type (TURTLE) comes out of his shell every so often (TURTLE),
22 Cowboy (FLY-BY-NIGHT) opens 15 across (opens ‘fly off the handle’ = FLY) for heartless (o) young man (‘boy’ without ‘o’ = BY) – he’s close to Bishop on board (‘knight’ is close to ‘bishop’ on chess board) we hear (=homophone indicator) (‘knight’ = ‘night’ = NIGHT) (FLY-BY-NIGHT),
24 Some upsetting (= reversal indicator) language vocalised (‘languagE VOCalised’ = evoc = COVE) in Safe Harbour perhaps (COVE),
25 Hasn’t been heard in Rome for a long time (OLD LATIN) and past one’s prime (OLD) in South America (LATIN America) (OLD LATIN),
26 Woods (FOREST) alarms the golfers (warning on the golf course = FORE-) on first two at St Andrews (first two at “ST Andrews” = -ST) (FOREST).
Down:
1 Stick up (AMBUSH) for Dawn (AM-) on transport (-BUS-) with hothead (‘Hot’ head = -H) (AMBUSH),
2 Clothing consumer (MOTH) taken in by upsetting (= reversal indicator) outlandish tomfoolery (‘outlandisH TOMfoolery’ = htom = MOTH),
3 Fair amount of (half of) dandelion, for example (weed) (half of ‘WEed’ = WE-), beside Crocosmia Lucifer, for instance (flower = -REWOLF) raised (= reversal indicator) (WEREWOLF) by a beastly monster (WEREWOLF),
4 An overseas hazard (iceberg / BERG) for those involved in December getaway (those involved in ‘DecemBER Getaway’ = BERG),
5 A subtle difference (NUANCE) to Mother Superior (nun = NU-N-) protecting a (-A-) church (Church of England = -CE) (NUANCE),
6 Can’t put it down (PAGE-TURNER) to pianist’s assistant? (PAGE-TURNER),
7 Stock options (GENE POOL) having all the characteristics you’d associate with family members in The House (GENE POOL),
13 Winter vehicle (SNOWMOBILE) for nurses finishing (‘nurseS’ finishing = S-) at the present time (-NOW-) and for those on call (-MOBILE) (SNOWMOBILE),
14 Trouble (= anagram indicator) those (those = ETHOS) with a belief system (ETHOS),
16 Time to give up (LENT) on fleur de lis (LILY) (LENT LILY) and wild daffodil (LENT LILY),
17 Make friends (HIT IT OFF) with crowd-pleaser (HIT) and one (I-) posh bloke (toff = -T OFF) (HIT IT OFF),
19 United States dismiss audits (‘United States’ dismiss ‘audits’ = nettes = TENETS) as ideology (TENETS),
21 Lush (LAVISH) birch (birch/whip = LA-SH) hanging over sign (-V- sign), for one (-I-) (LAVISH),
23 One of the people (GENT) in oxygen tent (in ‘oxyGEN Tent’ = GENT),
24 Maid from dramatic (‘maid’ from ‘dramatic’ ratc = CART) old vehicle (CART).