Across:
1 Type of business ('Small to Medium-sized Enterprise' = SME = S-ME) entertaining revolutionary (-CHE-) (SCHEME) plan (SCHEME),
4 Mixed (ASSORTED) with a (A-) society (-S-) model (-SORT-) and writer (-ED) (ASSORTED),
9 Foolish figure (ASS-) gets very good marks at university (1st = -IST) (ASSIST) with help (ASSIST),
10 Fears are (fears are) unnatural (= anagram indicator) (fears are = SEAFARER) to old sailor (SEAFARER),
12 Gets into Top Gear (DRESSES UP) with minis (DRESSES) on the increase (UP) (DRESSES UP),
13 Came around (AWOKE) to middle-class (middle ‘clAss’ = A-) taking Chinese pot (-WOK-) and drugs (-E) (AWOKE).
14 Sacking (FIRING) those in the kitchen (RANGES) (FIRING RANGES) where many pieces are used (FIRING RANGES),
18 Broadcast (air) on the radio (= homophone indicator) (‘air’ = ‘HEIR’) by secretary (PA) getting back (= reverse indicator) (PA = AP-) with father (-PARENT) (HEIR APPARENT) of man who’ll obviously succeed (HEIR APPARENT),
21 Pressure to dismiss rep (‘pressure’ to dismiss ‘rep’ = ssure = USERS) for consumers (USERS),
22 For example (e.g. = EG-), worker (-ANT-) in bar (line = -L-INE) (EGLANTINE) is a wild English rose perhaps (sweet brier/wild rose = EGLANTINE),
24 For each (PER-) court action (-SU-E) over advertisement (-AD-) (PERSUADE) for local, soft soap (local “soft-soap” = PERSUADE),
25 Hark back to the time (RECALL) when there was no wine in wine cellar (no ‘wine’ in ‘wine cellar’ = cellar = RECALL),
26 Dance for protestors (TOYI-TOYI) with one (-I-) plaything on either side (TOY-TOY-) touching his heart (‘hIs’ heart/ middle letter = -I) (TOYI-TOYI),
27 Fruitless, lacks fur (‘fruitless’ lacks ‘fur’ = itless = ISLETS)? Some islands! (ISLETS).
Down:
1 Give up one's seat (STAND-) at the start of 6 down (start of 'off-camera' = -OFF) (STAND-OFF) leading to impasse (STAND-OFF),
2 In (in) saying (= homophone indicator) (‘in’ = ‘inn’ = HOSTELRY) that, should offer one a drink (HOSTELRY),
3 They’re required (MUSTS) by those at the end of 15 down (end of ‘needs must’ = MUST-) going to school (-S) (MUSTS),
5 For those who want to retire but can’t? (SLEEPING PILL) As for the rest, some will be put out by this! (SLEEPING PILL),
6 Is not working (OFF-) for film producer (-CAMERA) (OFF-CAMERA) going there? To avoid getting shot! (OFF-CAMERA),
7 Blind panic (TERROR) on first tee (first ‘Tee’ = T-) leads to inaccuracy (-ERROR) (TERROR),
8 Tat from Rotterdam (‘tat’ from ‘Rotterdam’ = roerdm = DORMER) in the window (DORMER),
11 Put to work (USE-) by mate (FRIEND-) in Lebanon (Republic of Lebanon = RL = -R-L-) close to the money (close to the ‘moneY’ = -Y) (USER-FRIENDLY) with something that is idiot-proof (USER-FRIENDLY),
15 Can’t live without (NEEDS) grape juice (MUST) (NEEDS MUST) and it’s unavoidable (NEEDS MUST),
16 Think twice about (HESITATE) anaesthetist knocking out ants (‘anaesthetist’ knocking out ‘ants’ = aehetist = HESITATE),
17 Costly (STEEP-) for the French (‘the’ French = -LES) (STEEPLES) types over places of worship (STEEPLES),
19 In Paris where (French ‘where’ = OU-) time (-T-) and place (-PUT) (OUTPUT) is a measurement of one’s economic value (OUTPUT),
20 End of story (end of ‘storY’ = Y-) is ahead of its time (-EARLY) (YEARLY) for annual (YEARLY),
23 Opens 15 down (opens ‘needs must’ = NEEDS) for essentials (NEEDS).