Across:
1 Major states (POWERS) in 21 across ('power' = POWER-) taking direction (South = -S) (POWERS),
4 Unable to stand still (AGITATED), a (A-) soldier (-GI-) clearly said: (stated) “Head off !” (s) (‘stated’ without ‘s’ = -TATED) (AGITATED),
9 Head of CGT (head of ‘CGT’ = -C-) in foreign (= anagram indicator) union (union = NUN-IO) (NUNCIO) is a court official (NUNCIO),
10 1,000 (Roman 1,000 = -M-) at university (University of Limerick = -UL-) consumed by cacophony (noise) – “Up (= reverse indicator) (noise = E-SION) (EMULSION) Mayo!” (mayonnaise = EMULSION),
12 Hotel (H-) near Arles (Arles) is not finished (s) (‘Arles’ without ‘s’ = -ARLE-) on half of the quay (half of the ‘QUay’ = -QU-) popular (-IN) (HARLEQUIN) with a comic figure (HARLEQUIN),
13 Pressure (P-) to take drugs (-U-SE) over heart (heart/centre) complaint (centre of ‘compLaint’ = -L-) (PULSE)? Presumably, Garda is looking into that! (PULSE),
14 Force (POWER) from Kent, for instance (Cork’s Kent STATION) (POWER STATION), generates lots of energy (POWER STATION),
18 Agent (BROKER-) consumed by 1 across (‘powers’ = POWER -S) (POWER BROKERS) and people of influence (POWER BROKERS),
21 Opening 18 across (opening ‘power brokers = POWER)? Might! (POWER),
22 Spend too much time running (OVERTRAIN) to Guernsey to get away from veterinary surgeon (‘Guernsey’ to get away from ‘veterinary surgeon’ = vetrinaro = OVERTRAIN),
24 Tiny cast (tiny cast) touring (= anagram indicator) (tiny cast = SANCTITY) with A Life of Holiness? (SANCTITY),
25 A (A-) bad start (‘Bad’ start = -B-) for gents (-LOO-) from Central Germany (central ‘gerMany’ = -M) (ABLOOM) covered in Edelweiss, for instance (ABLOOM),
26 Leave it (STET-) to Mama’s Boys (-SONS) (STETSONS) in the broad-brimmed hats (STETSONS),
27 Performs like The King (REIGNS) producing Jazz (= anagram indicator) Singer (singer = REIGNS).
Down:
1 Donnybrook's (donnybrooks = PUNCH-UPS) boxers (pups = PU-PS) outside the Concert Hall (National Concert Hall = -NCH-) associated with University (-U-) (PUNCH-UPS),
2 The Casements (windows = WIND-OWS) cross river (-R-) (WINDROWS) to the lines of raked hay drying out (WINDROWS),
3 Her (her = RH-E) arrangement (= anagram indicator) includes popular (-IN-) (RHINE) flower (flower/river RHINE),
5 Some risk-takers are betting on those (GAMING-TABLES) local clashes (games = GAM-ES) over popular (-IN-) Government (-G-) Bill (-TAB-) from Labour leader (‘Labour’ leader = -L-) (GAMING-TABLES),
6 This is a long shot (TELEPHOTO lens) – ants accompanying elephants leave (‘ants’ accompanying ‘elephants’ leave = eleph = -ELEPH-) in toto? (T-OTO) (TELEPHOTO)
7 Sister-in-law ignores wines (‘sister-in-law’ ignores ‘wines’ = istrla = TRIALS) in cases (court cases = TRIALS),
8 The Yard (-Y) is after (= position indicator) gangster (DON-) from Kildare (-KE-) (DONKEY) for name of mule (DONKEY),
11 Putin (putin = PUT IN) welcomes most of them (most of ‘them’ = THE) from Wellington (wellington BOOT) (PUT THE BOOT IN) for kick about? (PUT THE BOOT IN),
15 Figures in The Inns (ROOM RATES) or Judge (rate = RATE-) in chambers (rooms = ROOM-S)? (ROOM RATES),
16 Mange (GET ALONG) to undo (= anagram indicator) long gate (long gate = GET ALONG),
17 Designed (= anagram indicator) man’s suit (man’s suit = TSUNAMIS) producing huge waves overseas (TSUNAMIS),
19 Resorts (spas = SPAS-) to initiating misery (initiating ‘Misery’ = -M-) on bender (-S bend) (SPASMS) with jerks (SPASMS),
20 Rachel comes out of cartwheeling (‘Rachel’ comes out of ‘cartwheeling’ = tweing = TWINGE) with sharp, sudden pain (TWINGE),
23 Lie (tale = TA-LE) about Bacharach’s intro (‘Bacharachs’ intro = -B-) (TABLE) produced for Arthur (Round TABLE / King Arthur at Camelot).