Across:
1 In Vogue (popular) dismissing upstart (‘up’ start = u) (‘popUlar’ without ‘u’ = POPLAR) in the forest (POPLAR tree),
4 One (I-) church (Church of England = -CE) reporter (CUB- reporter) with desk at the centre (‘dESk’ at the centre = -ES) (ICE CUBES) of the blocks of water coolers? (ICE CUBES),
9 Listen secretively to conversation of others (EARWIG) skint from water-skiing (‘skint’ from ‘waterskiing’ = waerig = EARWIG),
10 German (BERLINER) short (e) story (‘lie’ without ‘e’ = -LI-) set in European capital (capital of Switzerland = Berne = BER-NE-) at the end of winter (at the end of ‘winteR’ = -R) (BERLINER),
12 William, for example (William the CONQUEROR), from The Victor! (victor = CONQUEROR),
13 Permit (ALLOW) for two ports (two ports/lefts = -LL-) starting off (starting letter ‘Off’ = -O-) in Washington (WA = A-W) going all the way back (= reverse indicator) (ALLOW),
14 Trust (EXPECT-) a number of countries (nations) without a leader (n) (‘nations’ without ‘n’ = -ATIONS) (EXPECTATIONS) offering people hope (EXPECTATIONS)
18 It’s not left (RIGHT-) to Jack-of-all-trades (handyman) with no yard (y) (‘handyman’ without ‘y’ = -HAND-MAN) (RIGHT-HAND MAN) by Friday, for example? (Man Friday = RIGHT-HAND MAN to Robinson Crusoe),
21 Cover story (ALIBI) to drag out of Garibaldi (‘drag’ out of ‘Garibaldi’ = ibali = ALIBI),
22 Relents as (relents as) out (= anagram indicator) (relents as = ALERTNESS) in vigilant state (ALERTNESS),
24 Muscle contraction (T-IC) around head, ears (head of ‘Ears’ = -E-) leads to risky response (leads to ‘Risky Response’ = -RR-) – midwife (mid ‘wIFe’ = -IF-) (TERRIFIC) is marvellous! (TERRIFIC),
25 It’s incorporating a number of different elements (VARIED) for a diver (a diver) all at sea (= anagram indicator) (a diver = VARIED),
26 Presumably, the sort Humpty Dumpty and his ilk fell back on during hard times (NEST EGGS) or kept for the rainy days ahead? (NEST EGGS),
27 Screen for Gladiator (SHIELD) or The Guard (SHIELD).
Down:
1 Minister (PREACHER) with power (P-) to get through to (-REACH) one of those in hospital (-ER) (PREACHER),
2 Serves up (= reverse indicator) twirls (spins = -SNIPS) from batter (rap = PAR-) (PARSNIPS) and vegetables (PARSNIPS),
3 Delta (-D-) that is (i.e. = -IE-) in Australia (AU = A-U) (ADIEU) and so long (so long/goodbye = ADIEU),
5 Exonerated (cleared = CLEAR-ED) over an eyesore perhaps (-SIGHT-) (CLEAR-SIGHTED) – how perceptive is that? (CLEAR-SIGHTED),
6 Officer (colonel = COL-) fired from the army (-CANNON) (COLCANNON) for feeding this to the locals (COLCANNON),
7 Blow (BUNGLE) wind instrument (bugle = BU-GLE) holding top notes (top ‘Notes’ = -N-) (BUNGLE),
8 Barman (Senior Counsel = SC-) produces beers (brews) with no head (b) (‘brews’ without ‘b’ = -REWS) (SCREWS) for a number of twists (SCREWS),
11 It’s overwhelming (BREATHTAKING) snatching a bit of fresh air? (BREATHTAKING),
15 Judge (CRITIC-) is (-IS-) behind pilgrimage (behind/last letter of ‘pilgrimagE’ = -E) (CRITICISE) to Knock in the local sense (local ‘knock’ = CRITICISE),
16 Fool (IMBECILE) of doctor (-MB-) raises (= reverse indicator) vermin (lice = -ECIL-) in Ireland (.ie = I-E) (IMBECILE),
17 Ring (O-) denies (denies) adaptation (= anagram indicator) (denies = -NE-SIDE-) is primarily discriminatory (primarily ‘Discriminatory’ = -D) (ONE-SIDED) or lacking in balance (ONE-SIDED),
19 Make tracks (HASTEN) opening for Hothouse (opening for ‘Hothouse’ = H) Flower (aster) briefly (r) (‘aster’ without ‘r’ = -ASTE-) on first night (on first ‘Night’ = -N) (HASTEN),
20 Briefs (briefs) boss (= anagram indicator) (briefs = FIBRES) employed in the clothing industry (FIBRES),
23 Refuse (refuse/garbage = TRASH) initial treatment (initial ‘Treatment’ = T-) for reaction to poison ivy (-RASH) (TRASH).