Across:
8 Spring (SPA-) to retweet (retweet = -RT-) answer (-A) (SPARTA) from old city state (SPARTA),
9 Mature (OLD) climbers (VINES) (OLD VINES) could be responsible for 11 across, for instance (OLD VINES could be responsible for ‘Chardonnay’),
10 Held leaving New Delhi (‘held’ leaving ‘New Delhi’ = newi = WINE) port (WINE),
11 Mafia leader (-DON-) consumed by crazy (= anagram indicator) anarchy (anarchy = CHAR-NAY) (CHARDONNAY) – a variety such as what’s in 10 across (a variety such as what’s in ‘wine’ = CHARDONNAY),
12 Stature (stature/build = HEIGHT) of Henry (H-) VIII (-EIGHT) (HEIGHT),
14 Iodine (-I-) found in chopped up (= anagram indicator) elm (elm = L-ME), chestnut (chestnut TREE) (LIME TREE) and linden (LIME TREE),
15 Those in 10 across (‘wine’ = WINE-) found on ocean liner (sand = -S AND) with 26 across (‘spirit’ = SPIRIT-) and endless (end ‘lesS’ = -S) (WINES AND SPIRITS) types that are drunk (WINES AND SPIRITS),
18 Found down on the beach (S-AND-) hosting old (-O-) May Day appeal (mayday = -SOS) (SO-AND-SOS) for unnamed people with bad reputations (SO-AND-SOS),
20 Feel bitter about (RESENT) bank’s research department (banks ‘RESearch departmENT’ = RESENT),
22 A group of swimmers (SCHOOL- of fish) returning (= reverse indicator) dry (dry = Y-RD) around area (-A-) (SCHOOLYARD) synonymous with those taking a break from their education (SCHOOLYARD),
24 Coldplay ticket includes (‘coldplaY TICket’ includes = ytic) backtrack (backtrack = reversal indicator) (ytic = CITY) of “Amsterdam” (CITY),
25 Moving (= anagram indicator) camera (camera = MA-ACRE) captures old police force (-SS-) (MASSACRE) in Night of the Long Knives (Hitler’s June 1934 MASSACRE of the Brownshirts),
26 See 2 down.
Down:
1 Priest (priest) working (= anagram indicator) (priest = SPRITE) with amazing type who is a bit of a legend (SPRITE),
2 and 26 across: Sounds like drink is on the house (FREE SPIRIT) for one of the independents (FREE SPIRIT),
3 Pecan (pecan) nuts (= anagram indicator) (pecan = PANCE-) to go with starters of tenderloin terrine and (starters of ‘Tenderloin Terrine And’ = -TTA) (PANCETTA) cured pork (PANCETTA),
4 Musical conclusion (CODA) to part of Puerto Rico dance (part of ‘puerto riCO DAnce’ = CODA),
5 I’m dead (im dead) wrong (= anagram indicator) (im dead = AD IDEM) at a meeting of minds in Rome (AD IDEM),
6 Autographs (SIGNATURES) of most of (n) The Omen (‘sign’ without ‘n’ = SIG-) characters (-NATURES) (SIGNATURES),
7 Study (den = DE-N-) includes California (-CA-), Germany (Germany domain = .de = -DE-) and Middle Eastern (middle ‘easTern’ = -T) (DECADENT) type that’s corrupt (DECADENT),
13 One of the politicians (GREEN-) from Dáil Éireann (-HOUSE) (GREENHOUSE) is sowing the seeds of something big perhaps (GREENHOUSE),
14 Ate off isolated (‘ate’ off ‘isolated’ = isold = LIDOS) beaches on the Riviera (LIDOS),
16 Impossible to contradict (IRONCLAD) element (IRON-) at college (-C-) working with horses (-LAD) (IRONCLAD),
17 Is (-IS-) found in exhibition (exhibition/parade = PARAD-E) (PARADISE) of Utopia (PARADISE),
19 First class (SELECT) choice? (SELECT),
21 Fool (NITWIT) with identical twin dismisses nice lad (‘identical twin’ dismisses ‘nice lad’ = titwin = NITWIT),
23 Those drunk at the bar (ALES) are definitely not those in 15 across (ALES are not ‘wines and spirits’),
24 Sides with country cousin (sides with ‘COuntry cousIN’ = COIN) out of the capital (capital/money = COIN).