Across:
1 Bar (TAVERN) shady type (TA-N) over sending up (= reversal indicator) father (Rev = -VER-) (TAVERN),
4 Hound (hound = stalk = S- TALK) swallowed most of the hops (most of the ‘hops’ = -HOP) (SHOP TALK) – did you hear that at work? (SHOP TALK),
9 Soldier (-GI-) in gaol (gaol = LOG-A) break (= anagram indicator) (LOGGIA) found lying at the side of the house (LOGGIA),
10 Most of the cured meat (most of the ‘ham’ = HA-) from The Border (-END-) consumed by agents (CIA = C-IA) (HACIENDA) with ranch in Mexico (HACIENDA),
12 Old bookmaker (GUTENBERG) is a constituent in dough-making business (gluten) left (l) out (‘gluten’ without ‘l’ = GUTEN-) by Boris initially (‘Boris’ initially = -B-) and European Research Group (-ERG) (GUTENBERG),
13 English (E-) Times (-X-) has leaderless (f) column (‘file’ without ‘f’ = -ILE) (EXILE) with a sentence that’s obviously political (EXILE / deport is a political sentence/punishment),
14 Knows the origins of the great wave off Kanagawa (ART HISTORIAN knows the origins of Hokusai’s painting The Great Wave off Kanagawa) being an expert on The Liffey Swim (ART HISTORIAN),
18 Introduces 14 across (‘art historian’ = ART) to Reuters (Reuters = TRE-URES) Review (= anagram indicator) about Heads of Antiquities showcasing (heads of ‘Antiquities showcasing’ = -AS-) (ART TREASURES) the valuable objects of the museum (ART TREASURES),
21 Some flipping (= reversal indicator) high-risk rally (some flipping ‘high-risk rally’ = skral = LARKS) with carefree diversions (LARKS),
22 Relax (LIE AROUND) with a (A-) few drinks from the bar (-ROUND) after (= positional indicator) a whopper (LIE) (LIE AROUND),
24 English (E-) oxtail (‘ox’ tail = -X-) and stout (-PORTER) (EXPORTER) for overseas trader (EXPORTER),
25 Trade Union (TU-) to vote (-X-) to join English (-E-) party (-DO) (TUXEDO) – coming from the rag trade this is rather formal (TUXEDO),
26 Oriental (east = E-) state (= homophone indicator) plant (“sow” = “so” = S-O) admits pressure (-PRESS-) (ESPRESSO) can be stimulating (ESPRESSO),
27 Crazy (= anagram indicator) estate (estate = TEA SET) used by The Mad Hatters (TEA SET).
Down:
1 Vehicle (T-RAM) includes The Spanish (-EL-), for example (e.g. = -EG-) (TELEGRAM), in The Wire (TELEGRAM),
2 Do nothing (VEGETATE) to oppose (versus = V-), for example (e.g. = -EG-), engineer (-E-) responsible for 18 across, for instance (TATE responsible for ‘art treasures’ = -TATE) (VEGETATE),
3 Rule (REIGN) from base off Bering Sea (‘base’ off ‘Bering Sea’ = ering = REIGN),
5 Adam, presumably (HEAD GARDENER), is in charge of all the seed money (HEAD GARDENER),
6 Port (P-) and food (-RICE) with no starter (s) for lads’ nights out (‘stags’ without ‘s’ = TAGS) (PRICE TAGS) checked by the consumers (PRICE TAGS),
7 Relative (AUNTIE) gets a (A-) release (-UNTIE) (AUNTIE),
8 Rogues (KNAVES) offering key to open (‘key’ to open = K-) parts of the religious buildings (-NAVES) (KNAVES),
11 Driver’s aid (golf TEE-) is complete (-TOTAL-) cobblers (cobblers) for a fair amount (half of) (half of ‘cobblers’ = -LERS) (TEETOTALLERS) of those avoiding the demon drink (TEETOTALLERS),
15 Popular (IN) book (RESERVE) (IN RESERVE) on ice (IN RESERVE),
16 The rugby occasion opens (‘the rugby occasion’ opens = TRO-) for consumers (-USERS) (TROUSERS) covering both legs (TROUSERS),
17 Took drugs (USED) with Count (count/tot = TO -T) taking in island (I-) (USED TO IT) knowing the effects (USED TO IT),
19 Mysterious (= anagram indicator) legal (legal = ALLEG-) eagle (eagle) leading (e) (‘eagle’ leading = -E) (ALLEGE) claim (ALLEGE),
20 Support (PROP UP) in favour (PRO-) of little boxer (-P UP) (PROP UP),
23 Discourage removing acids (‘discourage’ removing ‘acids’ = courge = ROUGE) from French red wine (ROUGE).