Across:
1 Rust- (rust) -free (= anagram indicator) (rust = SU-TR-) around port (port/left = -L-) and yard (-Y) (SULTRY) – how is that not cool? (hot and humid = SULTRY),
4 Colourful type (EGGSHELL paint) provides protection for Humpty Dumpty presumably (EGGSHELL paint),
9 No hens in Lancashire? (no ‘hens’ in ‘Lancashire’ = lacair = RACIAL) It’s a cultural thing! (RACIAL)
10 Those working in the dead centre (CORONERS) of college (C-) or (-OR-) on (-ON-) hospital wards (ERs = -ERS) (CORONERS),
12 Do a job for (WORK-) Arabian (-HORSE) (WORKHORSE) or Trojan figure (WORKHORSE),
13 Blast from Bagatelle’s (‘blast’ from ‘Bagatelles‘ = gaele = EAGLE) score, of course? (EAGLE score on golf course),
14 It’s even more daft (dafter) losing the head (d) (‘dafter’ without ‘d’ = AFTER) (AFTERTHOUGHT) – giving a piece of one’s mind (-THOUGHT) with additional remark (AFTERTHOUGHT),
18 Local foolish person (GOOSE) spots (PIMPLES) (GOOSE PIMPLES) signs of excitement (GOOSE PIMPLES),
21 Metalworker lays down marker (‘metalworker’ lays down ‘marker’ = etlwo = OWLET) to young highflyer (OWLET),
22 Distribute (RATION-) beer (-ALE) (RATIONALE) in the case for …? (the case for = the RATIONALE for ...),
24 Foot the bill (PAY-) for mistakes (-SLIPS) (PAYSLIPS) – the ones the wages clerk is responsible for (PAYSLIPS),
25 Okinawa’s ability? Bottling (‘okinaWAS ABIlity’ bottling = wasabi = WASABI) tasty paste! (WASABI),
26 Chew the cud (chew the cud/contemplate = MEDITATE) as friend (mate = M-ATE) consumes mixed (= anagram indicator) diet (diet = -EDIT-) (MEDITATE),
27 Church office (VESTRY) opposed to (versus = V-) rest (rest) cure (= anagram indicator) (rest = -ESTR-)? Yes! (-Y) (VESTRY).
Down:
1 On the bottle and always twisted (SCREW CAP) – for those avoiding Cork, it's an alternative! (SCREW CAP),
2 Material (LACE-) in 23 down (orate) without a leader (o) (‘orate’ without ‘o’ = -RATE) (LACERATE) to rip apart (LACERATE),
3 Short (w) roasting (row) (‘row’ without ‘w’ = RO-) with a (-A-) constant (-C-) heat for starter (‘Heat’ for starter = -H) (ROACH) of fish popular with anglers (ROACH),
5 Handy entertaining prop’s (handy entertaining props = GLOVE PUPPETS) great (G-) desire (-LOVE) to punch (Punch of “Punch & July”= PUPPET-) scrum-half on the head? (‘Scrum-half’ on the head = -S) (GLOVE PUPPETS),
6 Some initially (‘Some’ initially = S-) make do (make do) working (= anagram indicator) (make do = -MOKED -A-) around hospital (H-) with Master (-M) (SMOKED HAM) – one of those already cured? (SMOKED HAM),
7 Primate leaves prayer meeting (‘primate’ leaves ‘prayer meeting’ = yereng = ENERGY) with type likely to light up the world (ENERGY),
8 Crafty type (boat/ship = -SS-) in River (River Lee = LE-E-) Erne – the first (‘Erne’ the first = -E) (LESSEE) one paying a flat fee perhaps? (LESSEE),
11 Large bunch of players (ORCHESTRA) reject (= reversal indicator) piece of advice (tip = PIT) (ORCHESTRA PIT) accommodating those on the fiddle and blowing their own trumpet (ORCHESTRA PIT),
15 WC (ROOM) /lavatory (toilet) doesn’t have one (i) (‘toIlet’ without ‘i’ = TO LET) (ROOM TO LET) that can be seen over the flat that’s unoccupied (ROOM TO LET),
16 Briefly (e) cheer up (cheer up/make happy = please) (‘please’ without ‘e’ = PLEAS-) worker (-ANT) (PLEASANT) in Nice (nice/agreeable = PLEASANT),
17 Bitterness, in a manner of speaking (ASPERITY), for a (A-) Pole (South Pole = -S-) contacting old Ruth (dated/old ‘ruth’ = P-ITY) Ward (-ER-) inside (ASPERITY),
19 Two (2) types of ceremony (‘pomp’ x 2) curtailed (p) (‘pomp + pomp’ without ‘p’ = POM-POM) for ball (POM-POM),
20 Competed (PLAYED) for place (-LAY-) in gym (PE = P-E-) on Open Day (open ‘Day’ = -D) (PLAYED),
23 Order (O-) from judge (-RATE) (ORATE) to speak up (ORATE).