Across:
1 One sharing the bill (CO-STAR) or expense (CO-ST-) on a (-A-) run (-R) (CO-STAR),
4 Butcher (= anagram indicator) curses ad (curses ad = USED CARS) for local bangers (USED CARS),
9 Expose lie (TRIP UP) around (= reversal indicator) place (put = T- UP) overlooking Split (split/tear = -RIP) (TRIP UP),
10 Quote out of context (MISSTATE), upsetting (= reverse indicator) card (SIM card = MIS-) from France, for one (-STATE) (MISSTATE),
12 Caught (C-) song (-A-RIA) reverberating around garden party (-FETE-) (CAFETERIA) in restaurant (CAFETERIA),
13 Discourage removing acids (‘discourage’ removing ‘acids’ = ourge = ROUGE) from nice red wine (ROUGE),
14 The accused (MAN IN THE DOCK) worker (MAN) nicked hot (nicked hot = IN THE DOCK) collection (= anagram indicator) (MAN IN THE DOCK),
18 From a haematological perspective, no mature DNA found in this vessel (RED BLOOD CELL) or crimson (RED) family (BLOOD) mobile in New York (mobile phone = CELL phone in US) (RED BLOOD CELL),
21 Awful (= anagram indicator) cost (cost = STO-C) around island (-I-) (STOIC) of crates from Mallus? (Crates of Mallus = a Stoic philosopher = STOIC),
22 A (A-) group of non-professional British Soldiers (Territorial Army/TA = -TA-) in The Voice (treble = TRE-BLE) (TREATABLE) deserving of attention in The Theatre (hospital theatre)? (TREATABLE),
24 They’re bound to sell (BOOKS-) on a short trip (-HOP) (BOOKSHOP) to a novel place? (BOOKSHOP),
25 Clip of (a) demanding type (diva) (‘Diva’ without ‘a’ = DIV-) having to cut (a) thesis (‘idea’ without ‘a’ = -IDE) (DIVIDE) in Split (DIVIDE),
26 Take another look at (REASSESS) judge (-ASSESS) behind (= position indicator) a bout (‘a bout’ = ‘about’ = RE-)? (REASSESS),
27 Ship (S-S) full of fish (-HAKE-) (SHAKES) sways from side to side (SHAKES).
Down:
1 Lost (= anagram indicator) coat (coat = TACO-) and money (-M-) in taxi (CA-B) (CATACOMB) or The Underground, of late (CATACOMB),
2 Hardens (STIFFENS) to small (S-) outburst of anger (fit) over (= reverse indicator) (fit = -TIF-) The Marshes (-FENS) (STIFFENS),
3 Mature (ADULT) soldier (lieutenant = -LT) follows (= position indicator) revolutionary (= reversal indicator) paramilitaries (Ulster Defence Association = UDA = ADU-) (ADULT),
5 Wasted in the body (SKIN AND BONES) of film (SKIN) on jazz (= anagram indicator) band (band = AND B-) individuals (-ONES) (SKIN AND BONES),
6 Gave up the ghost (died = DI-ED) over endless (end ‘lesS’ = -S-) capsized (= reverse indicator) freight (cargo) briefly (o) (‘cargo’ without ‘o’ = carg = -GRAC-) (DISGRACED) dragged through the mire (DISGRACED),
7 Presumably, you can count on this (ABACUS) key (music key A-) alternative lead (‘Alternative’ lead/first letter = -A-) to lead crystal (lead ‘Crystal’ = -C-) found in public transport (bus = -B-US) (ABACUS),
8 They’re all part of act (SCENES) for Mafia not taken in by misfeasance (‘Mafia’ not taken in by ‘misfeasance’ = sesnce = SCENES)
11 They’re out to stop the selling of alcohol, for instance, during dry periods (PROHIBITIONS), in bars (bars/bans = PROHIBITIONS),
15 The negative response (NO) to why it went wrong? (EXCUSES) (NO EXCUSES) Can’t complain about that! (NO EXCUSES),
16 Opens 18 across (opens ‘red blood cell = RED-) to get Adobe (Adobe = type of brick = - BRICK) (RED-BRICK) for English University (RED-BRICK),
17 They’re not up (SLEEPERS) the agents in The Waiting Game (SLEEPERS),
19 Boris (Boris) angry (= anagram indicator) (Boris = ISOBAR) about answer (-A-) (ISOBAR) – as the forecasters see it, it’s bound to bring its own pressure (ISOBAR),
20 Conspirator tears off strip (‘conspirator’ tears off ‘strip’ = CORONA) from The Sun (CORONA),
23 Steer clear of the High Street (‘steer’ clear of/ taken from the ‘High Street’ = hight = THIGH) for piece of chicken from the butchers (THIGH).