Across:
1 Most of (w) the row (‘row’ without ‘w’ = RO-) with a couple of firms (Co + Co = -COCO) (ROCOCO) is concerned with fussy architectural style (ROCOCO),
4 Commercial vehicle (STAFF CAR) for major employer (STAFF CAR for major employer/ army),
9 Circulates missing tale (‘circulates’ missing ‘tale’ = circus = CIRCUS) – the one with the clowns (CIRCUS),
10 Ruby (RED-) gets engineer (-E-) to stop (stop -SIGN) (REDESIGN) new plan (REDESIGN),
12 Explains the meaning (SEMANTICS) of virago falling off moving staircase (‘virago’ falling off ‘moving staircase’ = mnstaicse = SEMANTICS),
13 Coppers (PENCE) agree to leave Greenpeace (‘agree’ to leave ‘Greenpeace’ = npece = PENCE),
14 Plato (ANCIENT GREEK) was once the talk of the Mediterranean (ANCIENT GREEK),
18 Local quarrel (barney = B-ARNEY) crosses line (-L-) on small (= S-) pitch (pitch = -TONE) (BLARNEY STONE) – the visitors with the gift of the gab might have been touched by this (BLARNEY STONE),
21 One of the lads (chap = CH-AP) admits energy (-E-) (CHEAP) is not expensive (CHEAP),
22 Old people leaving church (old/archaic meaning: people who abandons religion = RENEGADES) heretics (RENEGADES),
24 Poison in (poison in = OPINIONS) cure (= anagram indicator) leads to convictions (OPINIONS),
25 A vicar (a vicar = CAVIAR) prepared (= anagram indicator) a fancy spread (a fancy spread = CAVIAR),
26 Showed indifference (SHRUGGED) mostly (y) reserved (‘shy’ without ‘y’ = SH-) for Rocky (-RUGGED) (SHRUGGED),
27 Take out (DELETE) Ted Lee (Ted Lee = DELETE) Duff (duff = anagram indicator).
Down:
1 Make a lot of noise (roar = RO- -AR) about one hundred (Roman 100 = -C-) thousand (informal 1,000 = -K-) and a fair amount of (half of) rest (half of ‘rest’ = ST-) (ROCK STAR) in the band playing music (ROCK STAR),
2 Mac’s rice (macs rice = CERAMICS) bake (= anagram indicator) produced in the oven (CERAMICS),
3 Flee from free lunch (‘flee’ from ‘free lunch’ = runch = CHURN) to make the butter (CHURN),
5 They look after Holly and Laurel (holly + laurel trees / TREE SURGEONS) in Cyprus (“Cyprus” = “Cypress” = TREE) it’s said (= homophone indicator), for those working in The Theatre (SURGEONS) (TREE SURGEONS),
6 Frank (FREE) Pound (pound/crush = PRESS) (FREE PRESS) had to keep mum in Stalinist Russia (FREE PRESS had to ‘keep mum’ / stay silent),
7 Club (C-) let in (let in = -LIENT) drunk (= anagram indicator) (CLIENT) regular (CLIENT),
8 The Messenger (messenger = RUNNER) found in Des Kelly’s? (RUNNER),
11 Drink (BITTER) order (O-) with selection (-RANGE) (BITTER ORANGE) of fruit (BITTER ORANGE),
15 Casting a shadow over (ECLIPSING) Oriental (east = E-) part of the film (-CLIP-) with local rat (informer / local ‘rat’ = -SING) (ECLIPSING),
16 Soldier (GI = G-I-) arrests elderly (-OLD-) Frenchman (Monsieur = -M-) with a fair amount of (half of) wine (half of ‘wine’ = -NE) (GOLD MINE) from lucrative venture (GOLD MINE),
17 Releases (SETS FREE) where one engages the props (props in SETS for plays) at the start of 6 down (‘free press’ = FREE) (SETS FREE),
19 Sounds like something you’d hear reverberating around an empty room (ECHOES) as Clare (CE = EC-) falls over (= reversal indicator) slippery (= anagram indicator) shoe (shoe = -HOES) (ECHOES),
20 Older sort (SENIOR) of address in Madrid (Senor = SEN-OR) protecting Third Reich (third ‘Reich’ = -I-) (SENIOR),
23 How is it great (G-) at dance party (-RAVE) (GRAVE) to be sober? (GRAVE).