Across:
8 Cost (PRI-CE) includes mean (mid point = n) lunch (mid point of ‘ luNch’ = -N-) (PRINCE) for regular at The Palace (PRINCE),
9 The virtues (angels / SERAPHIM) of Muriel and Ariel (Muriel and Ariel = angels = SERAPHIM),
10 Clare, for one (Clare Island = ISLE), immersed in tennis lesson (immersed in ‘tennIS LEsson’ = ISLE),
11 Admirer (fan = FA- N-) goes around African capital (capital/money = rand = -R AND) for musical ability (-EAR) (FAR AND NEAR) just about everywhere (FAR AND NEAR),
12 It follows, the question (ANSWER follows the question) is key (ANSWER),
14 Welcomes (USHERS IN) those putting them in their place (USHERS) up (= reversal indicator) north (NI = IN) (USHERS IN),
15 5 down (‘French’ = FRENCH) with most of 26 across (most of ‘onions’ = ONION) and 24 across (‘soup’ = SOUP) (FRENCH ONION SOUP) makes a nice starter? (Nice/French starter = FRENCH ONION SOUP),
18 Unable to tear myself away (IMMOBILE), as I’m (IM-) on the phone (-MOBILE phone) (IMMOBILE),
20 Intent (CANVAS in tent) of State (= homophone indicator) campaign? (‘canvass’ = ‘CANVAS’),
22 In the material sense, fine (fine/light fabric = DIAPHANOUS) director (D-) and agency (Associated Press agency = -AP-) worker (hand) briefly (d) (‘hand’ without ‘d’ = -HAN-) consumed by debts (IOUs = -I-OUS) (DIAPHANOUS),
24 Pressure (-P) follows woman (‘Sue’ = ‘sou’ = SOU-) on the radio (= homophone indicator) (SOUP) in trouble, as the saying goes (in trouble/ in the SOUP),
25 Take extra precautions (REINSURE) and listen (= homophone indicator) to weather forecast? (‘rain’ = ‘rein’ = REIN-)? Will do! (-SURE) (REINSURE),
26 Connoisseur lets out curse (‘connoisseur’ lets out ‘curse’ = onnois = ONIONS) bringing tears to many an eye (ONIONS).
Down:
1 Cream from Marine Corps (‘cream’ from ‘marine corps’ = rinops = PRISON) holding the POWS behind bars (PRISON),
2 Weekend (‘weeK’ end = K-) newspaper editor opens (‘Newspaper Editor’ opens = -NE-) English (-E-) (KNEE) joint (KNEE),
3 Leave (SET FORTH) Group (SET) is in favour of (FOR-) the (the) curtailment (e) (‘the’ without ‘e’ = -TH) (SET FORTH),
4 Setting up (= reversal indicator) some software support (some ‘softwaRE SUpport = resu = USER) for consumer (USER),
5 Type of toast (FRENCH toast), in a manner of speaking, in Canada (FRENCH),
6 This presumably isn’t designed to stop the record holders from leaving (OPEN PRISON) 23 down (‘open’ = OPEN) and 1 down? (‘prison’ = PRISON) (OPEN PRISON),
7 One (-I-) sheepish type (-RAM-) in odd-looking (= anagram indicator) suit (suit = TI-SU) (TIRAMISU) is sweet on one of those in Italian restaurant (TIRAMISU sweet/dessert),
13 You should be able to see through this (WINDOW PANE) advisory group (panel) briefly (l) (‘panel’ without ‘l’ = PANE) following (= positional indicator) Casement (casement WINDOW) (WINDOW PANE),
14 The bones (ULNAE) of what’s knocked about (= reversal indicator) in European luggage (in ‘EuropEAN LUggage’ = eanlu = ULNAE),
16 Didn’t leave the European Union, for instance (REMAINED), potentially? (= anagram indicator) NI – dear me! (NI dear me = REMAINED),
17 Celebration (OCCASION) of The Beano? (OCCASION),
19 Legendary victim (victim from legend = ICARUS) The Sun destroyed (ICARUS flew too close to the sun against his father’s advice),
21 Mid-January (mid ‘janUary’ = -U-) in Milan (Milan) training (= anagram indicator) (Milan = AL-MNI) (ALUMNI) past pupils (ALUMNI),
23 No salt in polentas? (no ‘salt’ in ‘polentas’ = poen = OPEN) Honest! (OPEN),
24 One Direction (south = S-) is massive (-HIP) (SHIP) taking the tour overseas (SHIP).