Across:
8 Not a large (MEDIUM) person sent for the messages (MEDIUM),
9 Ran wings (ran wings = WARNINGS) badly (= anagram indicator) getting a number of cautions (WARNINGS),
10 Donald (Donald DUCK) is out for nothing in particular (cricket out for nothing/nought = DUCK),
11 Stories ire (stories ire = ROTISSERIE) butchers (= anagram indicator) specialising in roasting cuts of meats (ROTISSERIE),
12 Ship (VESSEL) liar out of Versailles (‘liar’ out of ‘Versailles’ = vesles = VESSEL),
14 Run away (TURN TAIL) from convert, spy (convert spy = TURN) and detective (TAIL) (TURN TAIL),
15 Put on one’s guard by sportsmanship (GIVE FAIR WARNING) in 24 across (‘give’ = GIVE) impartial (FAIR) to most of 9 across (most of ‘warnings’ = WARNING) (GIVE FAIR WARNING),
18 Typical case (INSTANCE) of popular (IN-) attitude (-STANCE) (INSTANCE),
20 Wild (= anagram indicator) nectar (nectar = CRETAN) from a foreign island (CRETAN),
22 Points out problems (CRITICISES) to one (-I-) jerk (-TIC-) in major emergencies (CR-ISES) (CRITICISES),
24 Be generous (GIVE) to some revolutionary (= reversal indicator), authoritative vignette (some ‘authoritative vignette’ = evig = GIVE),
25 Most likely to get all steamed up (ANGRIEST) moving (= anagram indicator) inert gas (inert gas = ANGRIEST),
26 Lift lid off (d) casual drugs (‘downers’ without ‘d’ = OWNERS) for those legally in possession (OWNERS).
Down:
1 Be on the safe side (SECURE) with breakdown (= anagram indicator) rescue (rescue = SECURE),
2 Part of the column (DISK) is kid’s (kids = DISK) play (= anagram indicator),
3 Handy personal cover (UMBRELLA) is something to put away for a rainy day (UMBRELLA),
4 Powerful blow (SWAT) found in Washington’s Watergate (found in ‘Washington’s Watergate’ SWAT),
5 For removing the flaws, on paper (ERASER), of Harris Tweed with no width (‘Harris Tweed’ with no ‘width’ = arrsee = ERASER),
6 Old writer (Dante = D-ANTE) welcomes novel (= anagram indicator) title (title = -ILETT) (DILETTANTE) produced by one with superficial knowledge (DILETTANTE),
7 This will give you a start (IGNITION) or get you fired? (IGNITION),
13 Top actress (top actress = SPECTATORS) playing (= anagram indicator) to the audience (SPECTATORS),
14 Slice of dessert or tea brack (slice of ‘dessert or tea brack’ = TORTE) or rich cake (TORTE),
16 Unaware (IGNORANT) of upsetting (= reversal indicator) soldier (GI = IG-) by bringing up (= reversal indicator) broadcast (on = -NO-) with the sound off? (sound off = -RANT) (IGNORANT),
17 Forerunner (ANCESTOR) of crest on a (crest on a = ANCESTOR) dress (= anagram indicator),
19 McKinley releases my (‘McKinley’ ‘ releases ‘my’ = ckinle = NICKEL) overseas capital (US five-cent coin = NICKEL),
21 Sets up (= reversal indicator) last shot (last ‘shot’ = -T) for a couple of fathers (Rev + Da = revda = ADVER-) (ADVERT) in commercial (ADVERT),
23 Puts the building blocks in place (SETS) as witnessed in court (SETS witnessed in tennis court),
24 Warm (snug = GUNS) review (= reversal indicator) of pieces (GUNS).