Across:
1 Offshoot (BRANCH) of female support (BRA-) for concert hall (National Concert Hall = -NCH) (BRANCH),
4 Make a clean sweep (SANITISE) to debug the premises (SANITISE),
9 Nick (CUT-) Grant (grant/allow = -LET) (CUTLET) is flogged by the butchers (CUTLET),
10 Backs (= reversal indicator) civil disorder (riot = -TOIR) charge (tab = -BAT-) – it’s to do with a (A-) (ABATTOIR) scene of bloodshed (ABATTOIR),
12 Local subsidises (BANKROLLS) those with the dough (BANK-) for the baps and blaas (-ROLLS) (BANKROLLS),
13 Lift (RAISE) is (-IS-) in the middle of elevated (= reversal indicator) space for The Hearing (ear = RA-E) (RAISE),
14 Do some market research? (TEST THE WATER) Go take a running jump! (TEST THE WATER),
18 What a successful bounty hunter might do (CLAIM A REWARD) to contact the National Lottery Office? (CLAIM A REWARD),
21 Glamorous to release logs (‘glamorous’ to release ‘logs’ = amrou = AMOUR) of what’s essential to nice romance (what’s essential to Nice/France ‘romance’ = ‘love’ = AMOUR),
22 One of those on course (golf GREEN on golf course) raising (reverse indicator) Othello (Moor = - ROOM) (GREEN ROOM) in off-stage setting (GREEN ROOM),
24 Odd (= anagram indicator) thing (thing = NIGHT-) for accountant (-CA-) to post (-P) (NIGHTCAP) with late tot (tot/nip = NIGHTCAP)
25 Trouble (WAR-) about (-RE-) first novel (first ‘Novel’ = -N) (WARREN) set in The Maze (maze = WARREN),
26 Is (-IS-) found in exhibition (exhibition/parade = PARAD-E) (PARADISE) of Utopia (PARADISE),
27 Those providing the same line, time and again (CHORUS) or such (or such) trouble (= anagram indicator) (or such = CHORUS).
Down:
1 Produce spiteful criticism (BACKBITE) of support (BACK-) for Sting (sting = -BITE) (BACKBITE),
2 Tree (ash = A-SH) overlooking street (-ST-) and tops of neighbourhood including (tops ‘Of Neighbourhood Including’ (-ONI-) (ASTONISH) a maze? (‘a maze’ = ‘amaze’ = ASTONISH),
3 Heretic loses it (‘heretic’ loses ‘it’ = herec = CHEER) with Joy (CHEER),
5 Hasn’t a minute to spare (AS BUSY AS A BEE) to describe work ethic of Queen (AS BUSY AS A BEE),
6 Step in (INTERVENE) for referee (INTERVENE),
7 Creationist has no taste (‘creationist’ has no ‘taste’ = crioni = IRONIC) for what’s sarcastic (IRONIC),
8 It’s lax from Alexander (‘lax’ from ‘Alexander’ = eander = EARNED) – a reputation perhaps acquired deservedly (EARNED),
11 They’re designed for those approaching retirement (SLEEPING BAGS) or for those pitching temporary accommodation (SLEEPING BAG),
15 Turned a blind eye (TOLERATED) to what’s allowed (TOLERATED),
16 Party (LABOUR-) note (music note -E-) resistance (-R) (LABOURER) of one of the workers on site (LABOURER),
17 Bits and pieces (ODDMENTS) for eccentric (ODD-) blokes (-MEN-) on back (= reversal indicator) road (St = -TS) (ODDMENTS)
19 Worker (ant) falls over (= reversal indicator) (ant = -TNA-) in Cork (cap = CA-P) (CATNAP) – as a result of this, is unconscious briefly (CATNAP),
20 Takes up room (LODGER) in someone else’s house (LODGER),
23 What Dylan Thomas might have written about below (NEATH is the poetic term for below/beneath) in Wales (NEATH is in Wales).