Across:
1 Confirm (RATIFY) First Lady dropped LSD (‘first lady’ dropped ‘LSD’ = firtay = RATIFY),
4 Frenchman (Monsieur = -M-) consumed by tragic (= anagram indicator) murders (murders = DRUM-ERS) (DRUMMERS) of band members (DRUMMERS),
9 Part of the Volkswagen damaged (part of the ‘Volkswagen damaged’ = AGENDA) by list of items (AGENDA),
10 No sense in pseudoscience (no ‘sense’ in ‘pseudoscience’ = pudociec = OCCUPIED) when engaged (OCCUPIED),
12 The collective in old part of Russia (STATE FARM) and Ireland (STATE) with growing business (FARM) (STATE FARM),
13 Whet the appetite of (TEMPT) office worker (TEMP-) getting car (model -T) (TEMPT),
14 Blow (SOUND) the consequences (EFFECTS) (SOUND EFFECTS), as they’re responsible for creating noise and making a scene (SOUND EFFECTS),
18 CEO (chief executive officer = PRINCIPAL-) from City (city) loses head (c) (‘city’ loses ‘c’ = -ITY) (PRINCIPALITY) in Monaco (PRINCIPALITY),
21 Promote (BOOST) Kinky (= anagram indicator) Boots? (boots = BOOST),
22 Made less relaxed (TIGHTENED) by dental hygienist removing inlays (‘dental hygienist’ removing ‘inlays’ = detlhgenit = TIGHTENED),
24 Spicy type (CINNAMON) of con man in (con man in = CINNAMON) trouble (= anagram indicator),
25 It’s raw (fresh) for the most part (h) (‘fresh’ without ‘h’ = FRES-), and cold (-C-) going around (-O) (FRESCO) for the last supper, for instance (‘The Last Supper’ = FRESCO),
26 Shares (STOCK-) first (1st = -IST) (STOCKIST) place with plenty in reserve (STOCKIST),
27 Maurice (MO-E) takes in most of old European empire (most of ‘USSR’= -USS-) (MOUSSE) – it’s hair-raising stuff (MOUSSE).
Down:
1 Consider in a different light (REASSESS) most of (l) actual (“real” without “l” = REA-) engineering (-E-) found in two ships (SS-SS) (REASSESS),
2 Heat huge (heat huge = THE HAGUE) complex (= anagram indicator) in European city (THE HAGUE),
3 Legend (‘leg’ end = -G-) in disturbing (= anagram indicator) feud (feud = FUD-E) (FUDGE) gets to sit on the fence (FUDGE),
5 Opportunities for the Arabians to show how good they are at handling courses (RACE MEETINGS for Arabians /horses) with Irish (RACE) sessions (MEETINGS) (RACE MEETINGS),
6 Go up (MOUNT) summits of Everest, Trivor, Nuptse and (summits of Everest, Trivor, Nuptse and’ = ETNA) (MOUNT ETNA) one of the most active volcanos in the world? (MOUNT ETNA),
7 Force (-G- force) in Maine (Maine = ENI-MA) novel (= anagram indicator) (ENIGMA) provides a type of mystery (ENIGMA),
8 Teased (teased = SEDATE) criminal (= anagram indicator) with dope (SEDATE),
11 Stops working (MALFUNCTIONS) for most (e) stag (‘male’ without ‘e’ = MAL-) parties (-FUNCTIONS) (MALFUNCTIONS),
15 Tax (DIRT tax) what musicians make (TRACK) (DIRT TRACK) – that might need to be roughly road-tested first (DIRT TRACK),
16 Spike (PI-N-) welcomes a (-A-) number of honours from university (firsts = 1STS = -ISTS) (PIANISTS) for the musicians (PIANISTS),
17 Condition (SYNDROME) of some yobs needling democratic leaders (‘some yobs needling democratic’ leaders = SYND-) in Italy (-ROME) (SYNDROME),
19 Has an influence on the count (ABACUS), as what’s monitored is not in sodium carbonate (‘monitored’ is not in ‘sodium carbonate’ = sucaba = ABACUS),
20 Delivered (BORN-) by middle of September (middle of ‘September’ = -E-), order (-O) (BORNEO) to a primitive lad’s home perhaps (BORNEO),
23 Knocks back (= reversal indicator) old (-O) type of champagne (brut = TURB-) (TURBO) with one of those efficient types in a car (turbocharger = TURBO).