Across:
1 Single out (PICK-) the French (the = -LE) (PICKLE) in hot water (in a PICKLE),
4 Wild (= anagram indicator) pub dates (pub dates = BUDAPEST) in European capital (BUDAPEST),
9 Mole in (mole in = OILMEN) trouble (= anagram indicator) with crude types (OILMEN),
10 Too big for one boots (ARROGANT) in a (A-) tirade (-R-ANT) about tips for regulating overpowering government (tips for ‘regulating overpowering government’ = -ROG-) (ARROGANT),
12 Salad (= anagram indicator) eaters (eaters = EASTER), for example (e.g. = -EG-), get great (-G) (EASTER EGG) seasonal gift (EASTER EGG),
13 Subject (THEME) to helpmate getting rid of pal (‘helpmate’ getting rid of ‘pal’ = hemte = THEME),
14 Angriest riot (angriest riot = REGISTRATION) travelling (= anagram indicator) in front of the car (REGISTRATION),
18 Sounds like a lengthy queue in The Barracks (LONG DIVISION) for some of the tables (LONG DIVISION arithmetic tables),
21 Regret (regret) losing one’s head (r) (‘regret’ losing ‘r’ = EGRET) with flighty type (EGRET),
22 Carpets (RUNNERS -) for occupier, central (‘occupier’ central = -UP) (RUNNERS-UP) to those with second or third places (RUNNERS-UP),
24 Sanction (FINE) for a (A-) retweet (retweet = -RT-) from society (-S) (FINE ARTS) associated with paintings and sculpture (FINE ARTS),
25 Flower (flower/river PO-) from the countryside (-LAND) (POLAND) is for German neighbour (POLAND),
26 Produces the hits that are out of this world (ROCKETRY) for those aiming for the stars (ROCKETRY),
27 Casts a shadow over (SHADES) Dante’s ending (‘Dante’s’ ending = S-) in The Inferno (-HADES) (SHADES).
Down:
1 Drugs (-EE-) in prison (prison = PION-RS) changed (= anagram indicator) (PIONEERS) those who don’t take a drink (PIONEERS),
2 Describes (CALL S-) gin (gin = -IGN) cocktail (= anagram indicators) (CALL SIGN) for travellers over the airwaves (CALL SIGN identifies ship/plane on transmissions),
3 Gillespie drops lisp (‘Gillespie’ drops ‘lisp’ = gleie = LIEGE) in Belgium (LIEGE),
5 Honest (UPRIGHT) detective (PI-) leads a national operation (leads/first letters of ‘a national operation’ = -ANO) (UPRIGHT PIANO) for one of the big types that gets played (UPRIGHT PIANO),
6 Agricultural leader (‘agricultural’ leader = A-) behind (behind/support = FOR-) atrocious (= anagram indicator) riot (riot = -TIOR-) on island? (-I) (A FORTIORI) That’s the most convincing conclusion! (A FORTIORI),
7 Finish (ENAMEL) Le Mans (Le Mans) getting clipped (s) (‘Le Mans’ = without ‘s’ = leman = -NAMEL) by English leader (‘English’ leader = E-) going the wrong way (= reversal indicator) (leman + e ‘reversed’ = enamel = ENAMEL),
8 Ill-treated without Earl (‘ill-treated’ without ‘Earl’ = iltetd = TITLED) – the noble one (TITLED),
11 Whistleblower (REF-) gets to manipulate (-RIG-) Clio’s sister (-ERATO- one of The Nine Muses and Clio’s sister) at reading (from the 3Rs = -R) (REFRIGERATOR) place for those chilling (REFRIGERATOR),
15 Who averts (who averts = SHORT WAVE) trouble (= anagram indicator) for those in the broadcasting profession? (SHORT WAVE),
16 Emergency care (FIRST AID) for Irishmen (Irish ‘men’ = ‘fir’ = FIR-) on square (-T- square) in Egyptian port (Port Said = -S- AID) (FIRST AID),
17 Travelling (= anagram indicator) Spain (Spain = IN SPA-) and Germany (Germany domain = .de = -DE-) is top secret (top ‘secret’ = -S) it (IN SPADES) – to a very high degree, there’s a lot in it (IN SPADES),
19 Most of (e) the payment (most of ‘fee’ = -FE-) covered up by successor (HEI-R) (HEIFER) from farm (HEIFER),
20 Creationist has no taste (‘creationist’ has no ‘taste’ = crioni = IRONIC) for what’s sarcastic (IRONIC),
23 English (E-) policewoman (cop = -POC-) on the rise (= reversal indicator) headhunted (head ‘hunted’ = -H) (EPOCH) in memorable period? (EPOCH).