Across:
8 A series of steps (FLIGHT of steps) from nearly (s) all those closing 15 across (those closing 'domestic flights' = 'flights' without 's' = FLIGHT),
9 Housekeeper (DOMESTIC) opening 15 across (opening ‘domestic flight’ = DOMESTIC),
10 Contemplates (muses) avoiding 1000 (m) (‘muses’ without ‘m’ = USES) functions? (USES),
11 Symbolic stories (ALLEGORIES) in Friends (allies = ALL-IES) about awful (= anagram indicator) ogre (ogre = -EGOR-) (ALLEGORIES),
12 What’s wrong (BAD), for example (e.g. = EG-), with golf (golf = -G)? (BAD EGG) produced by scoundrel! (BAD EGG),
14 Detective (DI-) is like death warmed up (-SALLOW) (DISALLOW) in bar (bar/ban = DISALLOW),
15 Trouble at home (DOMESTIC) with lead, floor (lead letter on ‘Floor’ = F-) lamps (-LIGHTS) (DOMESTIC FLIGHTS), with local connections (DOMESTIC FLIGHTS),
18 Makes every effort (ATTEMPTS) to get top scorer (top ‘Scorer’ = -S) first (= position indicator) try (ATTEMPT-) (ATTEMPTS),
20 Half the gear (half the ‘GEar’ = -GE-) in public houses (bars = BAR-S) (BARGES) for those travelling around Rialto (BARGES for those travelling around Rialto).
22 Crazy (= anagram indicator) colonel (colonel = CON-OLLE-) welcomes retweet (rt = -TR-) backing (= reverse indicator) regiment (-R) (CONTROLLER) and company’s regulator (CONTROLLER),
24 It’s poetic – grass (literary/poetic ‘grass’ = LEA-) on the weekend (‘weeK’ end = -K) (LEAK) is an escape (LEAK),
25 Pardon (REPRIEVE) for a gent (‘a gent’ = ‘agent’ = REP-) writing (from the 3Rs = -R-) to one (-I-) First Lady (-EVE) (REPRIEVE),
26 Tests (TASTES) estate cars without taking care (‘estate cars’ without taking ‘care’ = estats = TASTES).
Down:
1 It's in the blood? (PLASMA) Raising (= reversal indicator) sheepish types (rams) off the summit (r) ('rams' without 'r' = ams = -SMA) on mountain! (alp = PLA-) (PLASMA),
2 Half of those in 12 across (half of ‘bad egg’ = EGG-) opening soon (opening ‘Soon’ = -S) (EGGS) with range of early birds? (EGGS),
3 State (= homophone indicator) Channel (channel = ‘strait’ = ‘STRAIGHT’) is only online? (STRAIGHT),
4 Characters taken in by unmelodious (characters taken in by ‘unmeLODIous’ = lodi) rebellious (= reverse indicator) (lodi = IDOL) celebrity (IDOL),
5 All backed (= reverse all indicator) leaders of General Assembly (leaders ‘General Assembly’ = ga = -AG-) in The House (semi = IM-ES) (IMAGES) pictures (IMAGES),
6 A (A-) street (-ST-) sweeper ultimately (‘sweepeR’ ultimately = -R-) with job (role = -ROL-E) taking in old (-O-), great (-G-) river (-R) (ASTROLOGER) is predictably a harbinger of things to come (ASTROLOGER),
7 Eliminated (WIPED OUT) model’s (models = anagram indicator) wide pout (wide pout = WIPED OUT),
13 Place in Dublin (Ely Place = EL-Y) takes in European (-E-) people (-MEN-) on boat (sailor = -TAR-) (ELEMENTARY) in a straightforward way (ELEMENTARY),
14 Knocks out local (‘knocks out’ locally = DECKS) wines out of wickedness? (‘wines’ out of ‘wickedness’ = ckeds = DECKS),
16 Old fashioned type (OUTMODED) in bloom (OUT-) and in vogue (-MODE-) on Dunmore Head (‘Dunmore’ head = -D) (OUTMODED),
17 In elite bar (elite bar), bubbly (= anagram indicator) (elite bar = LIBERATE) is free (LIBERATE),
19 Demonstrated (PROVEN) quietly (quietly/piano = P-) to raw beginner (‘Raw’ beginner = -R-) in the kitchen (-OVEN) (PROVEN),
21 Cleans up the childish mistakes (ERASER) for Regina (-R-) in flowing (= anagram indicator) saree (saree = E-ASER) (ERASER),
23 Flower (flower/River LEE-) from top soil (top ‘Soil’ = -S) (LEES) – the dregs of Bordeaux, for one (LEES found in Bordeaux/wine),
24 Group (LIST) no longer dismissed by Rolling Stone (‘no longer’ dismissed by ‘Rolling Stone’ = list = LIST).