Across:
8 Foams out of false bottom (‘foams’ out of ‘false bottom’ = lebtto = BOTTLE) in plastic container (BOTTLE),
9 Serving a (serving a = VINEGARS) drunk (= anagram indicator) a numbers of ciders, the fermented types (VINEGARS),
10 Included in formulae developed (included in ‘formulae developed’ = laed) going all the way back (= reversal indicator) (laed = DEAL) for work in the drugs trade (DEAL),
11 Studies (PORTRAYALS) of fish (-RAY-) caught in organised (= anagram indicator) patrols (patrols = PORT-ALS) (PORTRAYALS),
12 Worker’s leader (‘workers’ leader = W-) contacts major employer (-ARM-Y) around port (port/left = -L-) (WARMLY) in a kindly way (WARMLY),
14 I am (I’m = IM-) passing myself off as (-POSING as) (IMPOSING) being awesome (IMPOSING),
15 8 across (‘bottle’ = BOTTLE) with heads of fish (heads ‘of fish’ = OF) and most of 9 across (most of ‘vinegars’ = VINEGAR) (BOTTLE OF VINEGAR) is a staple of the chip shop (BOTTLE OF VINEGAR),
18 In retrospect (= reversal indicator), made tracks (ran = NAR-) with artist (-RA-) and tenor (-T-) or (-OR) (NARRATOR) with one of those doing voice-over (NARRATOR),
20 Half the biography (half the ‘life’ = LI-) doesn’t tell the truth (-LIES) (LILIES) of those who spent some time in the nursery perhaps (LILIES),
22 The allure (TEMPTATION) of off-colour (= anagram indicator) mint teapot (mint teapot = TEMPTATION),
24 One of the boys (WREN boys) or one of the birds? (WREN),
25 Permit (WARRANT-) is only for foundation (“only” for foundation = -Y) (WARRANTY) and might last a year if you’ve done a deal (WARRANTY),
26 One of The Shadows (SPIRIT) found in 8 across (SPIRIT found in ‘bottle’).
Down:
1 Best offer (best offer = BO-) for mature wine, for instance (aged = -DEGA), sent over (= reversal indicator) (BODEGA) by a Rioja producer (BODEGA),
2 Making a comeback (= reversal indicator) running behind (late = ET AL) the others in old Rome (ET AL),
3 They open (they open = NEOPHYTE) production (= anagram indicator) of The Apprentice (NEOPHYTE),
4 Nervous with no sun (‘nervous’ with no ‘sun’ = ervo = OVER) above (OVER),
5 Open (UNWRAP) to women (-W-) following (= positional indicator) a foreign (a = UN-) type of music (-RAP music) (UNWRAP),
6 Is this how you’d describe the awful accommodation of the man downstairs (the devil’s accommodation is UGLY AS HELL), as it’s not much to look at? (UGLY AS HELL),
7 Larks in a (larks in a = SRI LANKA) wild (= anagram indicator) island country (SRI LANKA),
13 GP, for example (Grand Prix = MOTORSPORT), drink (-PORT) drives (MOTORS-) from the start (= positional indicator) (MOTORSPORT),
14 Work out (INFER) for certain, actor is missing (‘for certain’ without ‘actor’ = ferin = INFER),
16 Oriental (east = E-) provides wrong (-X-) answer (-A-) in moral (moral = ORAL -M) exercise (= anagram) (ORAL EXAM) putting Chinese to the test (ORAL EXAM),
17 This has nothing to do (IDLENESS) with why someone can’t work out? (IDLENESS)
19 Glad to leave Stalingrad (‘glad’ to leave ‘Stalingrad’ = stinra = TRAINS) in coaches (TRAINS),
21 Cover of The Observer: (EYELID covers eye) “England (E-) to yield (yield = -YELID) erratically (= anagram indicator)” (EYELID),
23 Pass off displays (‘pass’ off ‘displays’ = dily = IDYL) as a pastoral view of America (IDYL / idyll),
24 Put on the back burner (WAIT) or give someone their dinner (serve = WAIT).