Across:
1 Upsets (= reversal indicator) shirty types (tops = -SPOT) working on paper (ed = DE-) (DESPOT) for tyrant (DESPOT),
4 Imagine (imagine = EMAI-ING) novel (= anagram indicator) about lost (-L-) (EMAILING) writing from surfing mecca? (writing from internet = EMAILING),
9 Criminal (= anagram indicator) dealer (dealer = LEADER) for The Don, for example (LEADER),
10 Next (ADJACENT) to Bill (AD-) on one side, Jack (on one side ‘Jack’ = -JA-) is one of those types that is spent (-CENT) (ADJACENT),
12 Dishy type (COLCANNON) of officer (COL-) gets fired from headquarters (-CANNON) (COLCANNON),
13 Foolish (INANE) characters embraced within a network (characters embraced ‘within a network’ = INANE),
14 Is responsible for 12 across, for instance (COOK is responsible for ‘colcannon’), found in the library (THE BOOKS) (COOK THE BOOKS) with fiddle (COOK THE BOOKS),
18 Synonymous of courtesy perhaps (GOOD BREEDING) you’d expect from the racy Arabians (racing Arabians/horses = GOOD BREEDING),
21 Aggressive introduction (‘aggressive’ introduction = A-) to address (-MISS) (AMISS) is inappropriate (AMISS),
22 May dreads (May dreads = DAYDREAMS) settlement (= anagram indicator) offering fanciful notions (DAYDREAMS)
24 Getting to know (LEARNING) fishy (= anagram indicator) angler (angler = LEARN-G) getting around up (= reversal indicator) North (NI = -IN-) (LEARNING),
25 Closing time? (BURIAL) That will be the death of you! (BURIAL),
26 Collaborated (ASSISTED) with a (A-) small (-S-), short (r) relative (‘sister’ without ‘r’ = -SISTE-) at the head (d) of Dwarfs (head of ‘dwarfs’ = -D) (ASSISTED),
27 Got the impression (SENSED) society (S-) needs (needs = -ENSED) changing (= anagram indicator) (SENSED).
Down:
1 Sensitivity (DELICACY) to gourmet food? (DELICACY),
2 Statuesque (-TALL-) in old Jerusalem (S-ION) (STALLION) stud (STALLION),
3 Some cabbage moth (some ‘cabbage moth’ = agemo) raised (= reversal indicator) (agemo = OMEGA) as the last in a series (OMEGA),
5 Cheers (MUD IN YOUR EYE) for the dirt (MUD) on where Iris might be (IN YOUR EYE) (MUD IN YOUR EYE),
6 Feeling the heat (IN A PICKLE) up the creek (IN A PICKLE),
7 It’s pleasant (nice) heading off (n) (‘nice’ without ‘n’ = ICE) with Gladstone (Gladstone BAG) (ICE BAG) for something to supress The Rising? (ICE BAG),
8 Gatecrasher misses races (‘gatecrasher’ misses ‘races’ = gaterh = GATHER) and rally (GATHER),
11 Broadcast (ON) first from bar (first from ‘bar’ = B-) and finished (-ENDED) from joint (KNEE joint) (ON BENDED KNEE) where one might deliver a proposal (ON BENDED KNEE),
15 Sound hats (sound hats = THOUSANDS) designed (= anagram indicator) by millenaries? (THOUSANDS),
16 ABCs, for instance (VITAMINS), of New (= anagram indicator) Nativism (nativism = VITAMINS),
17 Reports (= homophone indicator) row (“row” = “roe” = EGG S-) with a (-A-) young man (-LAD) (EGG SALAD) getting served in deli (EGG SALAD),
19 No Pinot in Appellation (no ‘Pinot’ in ‘appellation’ = apella’ = PAELLA) that’s a staple of Spanish restaurant (PAELLA),
20 Upsets (= reversal indicator) Slav- (Slav = -VALS) -Irish (-I-) by writing (from the 3Rs = R-) (RIVALS) to competitors (RIVALS),
23 Resolutely yells out (‘resolutely’ ‘yells’ out/ without ‘yells’ = reout = ROUTE), of course (ROUTE).