Across:
8 Tie up (ATTACH) that (that) mess (= anagram indicator) (that = ATT-H) overshadowing a (-A-) college (-C-) (ATTACH),
9 Works in 15 across (MILKMAID works in ‘milking parlours’) and in 24 across (‘milk’ = MILK-) and 24 down (‘maid’ = -MAID) (MILKMAID),
10 Laidback (= reversal indicator) characters from panel discussion (characters from ‘panEL DIscussion’ = eldi = IDLE) that’s not working (IDLE),
11 Reward for waiting (tip) up (= reverse indicator) (tip = PIT-) for Eliot (-TS- Eliot) coming from old Scottish borough (-BURGH) (PITTSBURGH) to industrial city in America (PITTSBURGH),
12 It’s trendy (popular) dumping uranium (u) (‘popular’ without ‘u’ = POPLAR) in the forest (POPLAR tree),
14 Lounges (PARLOURS) with uplifting (= reverse indicator) music (rap = PAR-) opening lots (opening ‘Lots’ = -L-) of whiskey cocktails (whiskey sours) starting off (s) (‘sours’ without ‘s’ = -LOURS) (PARLOURS),
15 Taking advantage of (MILKING) characters from 14 across (‘parlours’ = PARLOURS) (MILKING PARLOURS) in stockyards synonymous with Dexter’s family (MILKING PARLOURS synonymous with dexter cattle),
18 Sets up (= reversal indicator) experimental space (lab = BAL-) for stable characters (stable lads = -LAD-S) around One Direction (East = -E-) (BALLADES) producing romantic pieces of music (BALLADES),
20 Cider (cider) cocktail (= anagram indicator) (cider = DR- ICE) includes the last of the scrumpy (last of the ‘scrumpY’ = -Y-) (DRY ICE) – it’s provides a special effect (DRY ICE),
22 Drop a line (FISH) to one of those always on hand (FINGER) (FISH FINGER) or available in the convenience store (FISH FINGER),
24 Tap (tap/drain = MILK) one of those in 19 down similarly (one of those ‘drinks’ similarly = MILK),
25 Individual (ON-E-) covering fashion (fashion/style = -LOOK-) from centre of Paris (from centre of ‘Paris’ = -R) (ONLOOKER) for The Observer (ONLOOKER),
26 Television segment (CLIP-) is broadcast (-ON) (CLIP-ON) from conference? There is only one name for it! (CLIP-ON name tag).
Down:
1 Source from discourteous (‘source’ from ‘discourteous’ = ditous = STUDIO) drawing room? (STUDIO),
2 Limits calorie intake (limits ‘CAlorie intaKE’ = CAKE) in Madeira, for one (Madeira CAKE),
3 Church (CH-) primate (-APE-) starts reading out notices (starts ‘Reading Out Notices’ = -RON) (CHAPERON) from The Guardian (CHAPERON),
4 Fail to mention (OMIT) rise (= reverse indicator) in testimonials (in ‘tesTIMOnials’ = timo = OMIT),
5 Stuffier (CLOSER), cold (C-) and may be sore (sore -LOSER) (CLOSER),
6 Having the ability to fight The Plague (IMMUNOLOGY) – that’s what you expect from The Resistance (IMMUNOLOGY),
7 One of those staying around (LINGERER) to produce (= anagram indicator) Reeling (reeling = LINGE-ER) Around Last Year (last ‘yeaR’ = -R-) (LINGERER),
13 In all probability (LIKELIHOOD), took a shine to (LIKE-) Hook briefly (‘Hook’ briefly = -HOO-) in Cork (cork/ ‘lid = -LI-D) (LIKELIHOOD),
14 Carries water (PIPE-) from top of Slievenamon’s (top of ‘Slievenamons’ = -S) (PIPES) cylindrical veins of rock (PIPES),
16 One (I-) atlas in (atlas in = -TALIANS) production (= anagram indicator) (ITALIANS) for the Austrian neighbours (ITALIANS),
17 Revolutionary (RED-) court (-CT) is behind (= position indicator) fury (-IRE-) (REDIRECT) to shoot the main players again perhaps (REDIRECT film),
19 Madeira’s (DRINKS) ports? (DRINKS),
21 Charlie (C-) Grant (-ALLOW) (CALLOW) is an inexperienced type of youth (CALLOW),
23 Blood and guts (GORE) in the extremes of gothic architecture (the extremes of ‘GOthic architectuRE’ = GORE),
24 Escaped from aides-de-camp (‘escaped’ from ‘aides-de-camp’ = aidm = MAID) with the help of the Big House (MAID).