Across:
8 Bosses (CHIEFS) ran away from franchise (‘ran’ away from ‘franchise’ = fchise = CHIEFS),
9 Keep under control (RESTRAIN) with Cross (= anagram indicator) Trainers (trainers = RESTRAIN),
10 They typically spend adult life on land before returning to sea (EFTS), escaping from the sun, for starters (‘Escaping From The Sun’ for starters = EFTS),
11 Those in charge (EXECUTIVES) of the suits (the suits = EXECUTIVES),
12 New (= anagram indicator) purse (purse = SUPER-) for top boxer (top ‘Boxer’ = -B) (SUPERB) is remarkable (SUPERB),
14 Writer (pen) briefly (n) (‘pen’ without ‘n’ = -PE-) consumed by sci-fi (sci-fi = S- CIFI-) compilation from the start (‘Compilation’ from the start = -C) (SPECIFIC) is very particular (SPECIFIC),
15 Most of those in 8 across (most ‘chiefs’ = CHIEF) and 11 across (‘executives’ = EXECUTIVES) (CHIEF EXECUTIVES) minding their own businesses presumably (CHIEF EXECUTIVES),
18 Engineering (E-) movement’s (movements = -MOTIONS) (EMOTIONS) strong feelings (EMOTIONS),
20 Did a job directing (FILMED) Frenchman (Monsieur = -M-) in field (field = FIL-ED) work? (= anagram indicator) (FILMED),
22 One (I-) writing (from the 3Rs = -R-) with both feet on the ground (-RATIONAL) (IRRATIONAL) is absurd (IRRATIONAL),
24 Some of the local stick (BOSS is part of hurley stick) similar to one of those in 8 across (BOSS is similar to one of the ‘chiefs’),
25 Artist impressions (OUTLINES) of holiday (OUT-) bars (-LINES) (OUTLINES),
26 You’re unlikely to hear this praise if you’re late (EULOGY), as typically it accompanies a put down (EULOGY).
Down:
1 There’s no cure for this (THE FLU) heartless (heartless/remove centre = i) thief (‘thief’ without ‘i’ = THE F-) turning over (= reversal indicator) university (University of Limerick = UL = -LU) (THE FLU),
2 ABC (music keys & typing keys : KEYS) of Florida? (Florida KEYS),
3 Labs seem (labs seem = ASSEMBLE) unreliable (= anagram indicator) to construct (ASSEMBLE),
4 Needs no introduction (p) to Free (‘purge’ without ‘p’ = URGE) Press (URGE),
5 Provide cover for (ASSURE) foolish type (ASS-) heading off (c) to smoke (‘cure’ without ‘c’ = -URE) (ASSURE),
6 CIA airlift (CIA airlift = ARTIFICIAL) explosive (= anagram indicator) that’s of a synthetic nature (ARTIFICIAL),
7 Love (LIKE-) sage (-WISE) (LIKEWISE) in the same way (LIKEWISE),
13 Let out (-VENT-) in the community (European Union = E-U-) with friend (-ALLY) (EVENTUALLY) sooner or later (EVENTUALLY),
14 Female (SHE-) detective (-DS) (SHEDS) removes furs (SHEDS),
16 Funny (HUMOROUS) organic matter (humus = HUM-US) found around summits with old rocky outcrops (summits with ‘Old Rocky Outcrops’ = -ORO-) (HUMOROUS),
17 Organisation (United Nations = UN-) didn’t see in a handy way (didn’t see hand in cards/poker = -FOLDED) (UNFOLDED) how the development finished up (UNFOLDED),
19 Having the knowledge (know one’s ONIONS) of edible bulbs (ONIONS),
21 Flag (ENSIGN) a number of points (east + north = E+N = EN-) for one of the Languages (-SIGN language) (ENSIGN),
23 Those characters in the casino sensitive (those characters in the ‘casiNO SEnsitive’ = NOSE) to what’s on the plane (NOSE on plane/aeroplane),
24 Bishop (B-) is not in good shape (-ILL) (BILL) making way through the house (BILL making way through The House/Dáil).