Across:
1 Part of dance (STEP-) exercise (-PE) (STEPPE) in large flat space (STEPPE grasslands),
4 Massive (COLOSSAL) tax write-off (-LOSS-) consumed by one of those in the pit (CO-AL) (COLOSSAL),
9 Serge’s (serges = EGRESS) adaptation (= anagram indicator) is way out (EGRESS),
10 Etching a (etching a = TEACHING) model (= anagram indicator) working at a fellow’s place (university fellow = TEACHING),
12 One of those from Irish kitchen (COLCANNON) in the army (colonel = COL) is likely to be fired (-CANNON) (COLCANNON),
13 Race (EVENT) of sailor isn’t part of revelations (‘sailor’ isn’t part of ‘revelations’ = EVENT),
14 Unimportant people (LIGHTWEIGHTS) throwing digs at people in Ring (LIGHTWEIGHTS),
18 There won’t be any jam produced in this (no traffic jam in LIGHT TRAFFIC) business (TRAFFIC) following (= positional indicator) most of 8 down (most of ‘lights’ = LIGHT) (LIGHT TRAFFIC),
21 First Picasso (first ‘Picasso” = P-) in nude (nude = U-END) form? (= anagram indicator) (UPEND) Flip! (UPEND),
22 Duck starter (‘duck’ starter = D-) with fish (-RAY) and a type of meat (HORSE meat) (DRAY HORSE) – you could pull a wagon if you had that (DRAY HORSE),
24 Height (height = HIGH TE-) applied (= anagram indicator) to church (-CH) (HIGH TECH) using modern gadgetry (HIGH TECH),
25 Quarrel (F-IGHT) is over writing (from 3R’s = -R-) (FRIGHT) that will give one the heebie- jeebies (FRIGHT),
26 One of the old coppers (old copper = penny = P-) with talent (talent = -ATENTL-) working (= anagram indicator) for The Yard (-Y) (PATENTLY) obviously (PATENTLY),
27 In the autumn (SEPT-), one (-I-) cold (-C) (SEPTIC) could be infectious (SEPTIC).
Down:
1 Outlines the characters (STENCILS) with awkward (= anagram indicator) client (client = -TENCIL-) in ship (S-S) (STENCILS),
2 They restrict the noise (EARPLUGS) in sound systems? (EARPLUGS),
3 Covered-up a Shakespearean (covered ‘up a Shakespearean’ = PASHA) character with Ottoman roots (PASHA),
5 One of those successes (OVERNIGHT success) following a (B- follows ‘a’) meeting at the bar (Attorney General = -AG) (OVERNIGHT BAG) gets carried away with business trip (OVERNIGHT BAG),
6 Killer whale (ORC-A) circles that man (-HE-) with a fair (half of) stroke (half of ‘stroke’ = -STR-) (ORCHESTRA) – get them to play that music from Jaws, for instance (ORCHESTRA),
7 Old man gets out of Promised Land (‘old man’ gets out of ‘Promised Land’ = prised = SPIDER) – you can see it on The Web (SPIDER),
8 Quintet from 14 across opening (‘lightweights’ = LIGHT-) for One Direction (south = -S) (LIGHTS) could be beacons of illumination (LIGHTS),
11 Organisation (UN-) is organised (-METHODICAL) (UNMETHODICAL) by sloppy type (UNMETHODICAL),
15 How judge judged criminal (TRIED) charged (ion = -I ON) over initial theft? (initial ‘theft’ = -T) (TRIED IT ON) Assessed the suit! (tried on suit of clothes = TRIED IT ON),
16 Foreign footballers (FA = AF-) retiring (= reversal indicator) to 25 across (‘fright’ = -FRIGHT) (AFFRIGHT) is alarming (AFFRIGHT),
17 Catholic (catholic/diverse = ECLECTIC) comprehensive? (ECLECTIC),
19 Keep that under your hat (HUSH UP) or veil? (veil/conceal = HUSH UP),
20 Woman (W-) with skater’s figure (figure of -EIGHT) (WEIGHT) is a concern for dieter (WEIGHT),
23 Finishes 22 across (‘dray horse’ = HORSE) with nag (HORSE).