Across:
1 Part of dance (STEP-) exercise (-PE) (STEPPE) in large flat space (STEPPE grasslands),
4 Is this what happened to grandfather (clock) when not working (LOST TIME) at sea? (LOST) Those inside will get this! (TIME) (LOST TIME),
9 Going through a rough patch (UNEVEN) as not going steady? (UNEVEN),
10 Ten girls (ten girls) out (= anagram indicator) (ten girls = STERLING) of First Class (first-class = STERLING),
12 Sack (BAG-) American (-A-) writers (writers) central (t) (‘wriTers’ central = -T-) to fashion magazine (-ELLE) (BAGATELLE) or is it not worth mentioning? (BAGATELLE),
13 Some complex conservative (some ‘complEX CONservative’ = EX-CON) has a reputation for finishing sentences? (EX-CON),
14 Ask St Anthony to help with this (LOST PROPERTY) opening 4 across (opening ‘lost time’ = LOST) on the estate? (PROPERTY) (LOST PROPERTY),
18 Excessively proud (VAINGLORIOUS) to report (= homophone indicator) blood line (‘vein’ = ‘vain’ = VAIN-) is linked to a striking beauty (-GLORIOUS) (VAINGLORIOUS),
21 No trust in truth serum (no ‘trust’ in ‘truth serum’ = herum = RHEUM) as it’s a watery fluid, in the literary sense (RHEUM),
22 Court case (trial = T-RIAL) involving orchestral leader (‘Orchestral’ leader = -O-) from NSO (-NSO-) (TONSORIAL) relates to The Barber of Seville perhaps in a funny way? (TONSORIAL),
24 Sharp (QUICK) cement (FIX) (QUICK FIX) – that’ll do a job but not for long (QUICK FIX),
25 Distinguished scientist (SAVANT) designed (= anagram indicator) Sat Nav (satnav = SAVANT),
26 It’s for the actor (ST-AGE) holding sweetheart (‘swEet’ heart = -E-) with hesitation (-ER-) (STEERAGE) in Titanic, for one (STEERAGE),
27 Rely on (DEPEND) Germany (Germany domain = .de = DE-) taking power (-P-) at last (-END) (DEPEND).
Down:
1 Most of (d) the team (‘squad’ without ‘d’ = SQUA-) from hostelry (B&B = -BB-) with endless (t) accommodation (‘let’ without ‘t’ = -LE) (SQUABBLE) in row (SQUABBLE),
2 Greene is (Greene is) stupid (= anagram indicator) (Greene is = ENERGISE) to get a shot in the arm (ENERGISE),
3 Helpmate drops hem (‘helpmate’ drops ‘hem’ = lpate = PLEAT) from the fold in the skirt (PLEAT),
5 Breaking down (ON THE DECLINE) what it means to go to The Dogs (ON THE DECLINE),
6 The Hill (TOR-) is trying to get the best out of the team (-MENTOR) (TORMENTOR) by making others suffer (TORMENTOR),
7 Nearly (t) fool (‘idiot’ without ‘t’ = IDIO-) heartless (heartless/remove centre = ‘r’) Bellow (‘cry’ without ‘r’ = -CY) (IDIOCY) by acting stupid (IDIOCY),
8 There’s no art found in Argentine (no ‘art’ found in ‘Argentine’ = genine = ENGINE) after search on the internet? (internet search ENGINE),
11 Everyone (ALL) is in favour of (for) heading off (f) (‘for’ without ‘f’ = -OR-) to night on (night on) set (= anagram indicator) (night on = NOTHING) (ALL-OR-NOTHING) of Uncompromising Extremes (ALL-OR-NOTHING),
15 Beckett, for one (PLAY MAKER), is an expert at engineering a score? (football PLAYMAKER),
16 Admit one (admit one = DOMINATE) criminal (= anagram indicator) with influence (DOMINATE),
17 Lose it (lose it) wildly (= anagram indicator) (lose it = ISOL-TE-) over a (-A-) key (music key -D) (ISOLATED) to remote (ISOLATED),
19 Paramilitaries’ (IRA-) top quartermaster (top ‘Quartermaster’ = -Q-) is (-IS) (IRAQIS) living in the Middle East (IRAQIS),
20 Check for accuracy (vet) clip (t) (‘vet’ without ‘t’ = VE-) on the Mediterranean coast (-NICE) (VENICE) or on the Adriatic (VENICE),
23 Order (O-) from judge (-RATE) (ORATE) to speak up (ORATE).