Across:
8 It’s a risky business (CASINO) for egomaniacs losing game (‘egomaniacs’ losing ‘game’ = oniacs = CASINO),
9 Answer (A-) – well it’s not (-ILL-) in new (= anagram indicator) X-ray (xray = -X-ARY) (AXILLARY) relating to the armpit (AXILLARY),
10 The first four characters in 22 across (first four characters in ‘wallpapers’ = WALL) – a product of The Masons (WALL),
11 To sing from the same hymn sheet (KEEP IN TUNE), learn your numbers correctly (KEEP IN TUNE),
12 Graduate (-BA-) in capital (cash = -CAS-H) (CASBAH) with citadel (CASBAH),
14 Nurses go (nurses go) out (= anagram indicator) (nurses go = SURGEONS) with doctors in the theatre (SURGEONS),
15 Ran off with (MISAPPROPRIATED) young woman (miss) briefly (s) (‘miss’ without ‘s’ = MIS-) with right- (-APPROPRIATE-) -wing dictator? (wing/side of ‘Dictator’ = -D) (MISAPPROPRIATED),
18 Make known (DISCLOSE) this is one (-I-) top slammer (top ‘Slammer’ = -S-) in DC (D-C-) to escape from (-LOSE) (DISCLOSE),
20 No matter – it’s not part of shock treatment (‘no matter’ it’s not part of ‘shock treatment’ = shckte = SKETCH) by design (SKETCH),
22 Those in The House covering-up Partition (WALLPAPERS) with report (-PAPER-) dividing those in The Maze (walls = WALL-S) (WALLPAPERS),
24 Sign (OMEN) is a bit gruesome (a bit ‘gruesOME Nevertheless’ = OMEN),
25 County (DOWN-) Tipperary (T-) has an old city (-UR-) with new (-N) (DOWNTURN) economic problem (DOWNTURN),
26 Enthuse ((EXCITE) with final (= position indicator) quote (-CITE) from former partner (EX-) (EXCITE).
Down:
1 Unmanageable without legume (‘unmanageable’ without ‘legume’ = nanaab = BANANA) or fruit (BANANA),
2 Medicinal herb (DILL) for some induced illness (some ‘induceD ILLness’ = DILL),
3 You’ll find those at school (BOOKS-) going on the mitch (mitch/truant = going on the -HOP) (BOOKSHOP) to a novel place? (BOOKSHOP),
4 Bitterness (RAGE) on the finish of 6 down (the finish of ‘all the rage’ = RAGE),
5 Slicker (OILIER) fiction (-LIE-) in Republic of Ireland (ROI) rewritten (= anagram indicator) (ROI = OI-R) (OILIER),
6 Every ounce of anger (ALL THE RAGE) in Vogue (in vogue = ALL THE RAGE),
7 Gets fired (artillery = ORDNANCE) by those in Arsenal (arsenal/collection of weapons = ORDNANCE),
13 You’d expect to find detectives at end of this (BRANCH LINE) secondary route from station (secondary railway line = BRANCH LINE),
14 Wiggle room (SCOPE) in terms of reference? (SCOPE),
16 Plagiarist (IMITATOR) is not capable of anything original (IMITATOR),
17 Refused to accept (RESISTED) desert is (desert is) contaminated (= anagram indicator) (desert is = RESISTED),
19 Ring (O-) Panama (-PA-) and Quebec (Quebec = -QUE) (OPAQUE), as it’s not clear (OPAQUE),
21 Produce (CREATE) from area (-A-) within Mediterranean island (CRE-TE) (CREATE),
23 No grain in Argentina (no ‘grain’ in ‘Argentina’ = enta = ETNA) or Sicilian hot spot (ETNA),
24 Dante isn’t involved in headcount (‘Dante’ isn’t involved in ‘headcount’ = hcou = OUCH) and that hurts (OUCH).