Across:
8 You’d expect to find this in 4 down (POTATO found in ‘beds’) for Spud (POTATO),
9 It’s the type of music (ELEVATOR music) that has its ups and downs (ELEVATOR),
10 No basil in Islamabad (no ‘basil’ in ‘Islamabad’ = ADAM) for the gardener (ADAM),
11 Can siestas (can siestas = ASSISTANCE) work (= anagram indicator) for those who need a helping hand? (ASSISTANCE),
12 Source of honour (CREDIT) to direct (direct = CREDIT) Rocky (= anagram indicator),
14 Polish (-SHINE) paper (The Sun = SUN-) from the start (= positional indicator) (SUNSHINE) could be under a cloud (SUNSHINE),
15 Eccentric (CHARACTER-) is first (first = 1st = -IST-) to get fair amount of (half of) the basics (half of the ‘basics’ = -ICS) (CHARACTERISTICS) and a number of the elements (CHARACTERISTICS),
18 Did time in detection centre perhaps (EDUCATED) and learned a lesson (EDUCATED)
20 Part of the diagnosis terrified (part of the ‘diagnosis terrified’ = SISTER) one of the family members (SISTER),
22 Flat (HORIZONTAL) is laid out on one level (HORIZONTAL),
24 Casing for handling long-term (casing for ‘handling long-term’ = HARM) injury (HARM),
25 Senses (MEANINGS) popular (-IN-) legend (“leg” end = -G-) consumed by wealth (means = MEAN-S) (MEANINGS),
26 Engineering (E-) a (-A-) bizarre (= anagram indicator) rise (rise = -SIER) (EASIER) is getting less difficult (EASIER).
Down:
1 Came in first (WON-) with the foreign (the = -DER) (WONDER) phenomenon (WONDER),
2 Has a hand (PALM) in finding characters in Oedipal mystery (finding characters in “Oedipal mystery” = PALM),
3 In the idealistic sense, Don Quixote is one (ROMANTIC) living in Italy (ROMAN-) with a short (e) name (cite) on reflection (= reversal indicator) (‘cite’= ‘etic’ without ‘e’ = -TIC) (ROMANTIC),
4 Nightspots (BEDS) for the kings and queens (BEDS),
5 Orson Welles dismisses lower (‘Orson Welles’ dismisses ‘lower’ = osnles = LESSON) class type (LESSON),
6 A US chapter (A US chapter = PARACHUTES) rewritten (= anagram indicator) for those in Skyfall (PARACHUTES),
7 Is capable of fiery outbursts (VOLCANIC) with vice chancellors getting rid of lechers (‘vice chancellors’ getting rid of ‘lechers’ = viccanlo = VOLCANIC),
13 Guidelines (DIRECTIONS) from alternative (= anagram indicator) Nordic site (Nordic site = DIRECTIONS),
14 The going rate (SPEED) for drugs? (SPEED),
16 Some of the water (HYDROGEN and oxygen make up water) on the top of the table is the first one you’ll see (on the top of the Periodic Table, HYRDOGEN is No 1),
17 Put down (INSULTED) writer (-ED) after (= positional indicator) abusive remark (INSULT-) (INSULTED),
19 The prickly types (THORNS) in North’s (norths = THORNS) Order (= anagram indicator),
21 Academic (learned) lost the head (l) (‘learned’ without ‘l’ = EARNED) and got what he deserved, financially speaking (EARNED),
23 Caretakers with no career (‘caretakers’ with no ‘career’ = taks = TASK) or something to do (TASK),
24 Put on (HOST) old (-O-) substitute initially (‘substitute’ initially = -S-) during interval (half-time = H-T) (HOST).