Solution to 20D has been deliberately left unsolved and is to be answered by a non-regular/novice commenter, with proper annotation. Those who have answered earlier in the week, please give others a chance.
Open for anyone to answer, if not solved by 1 PM.
ACROSS
1 Plasticine managed to protect films (6) CINEMA [T]
5 Grade repeated often, it's observed? (8) REGARDED Letter Bank
9 These drill masters go about doing tests? (8) DENTISTS {DENTISTS+GO}*=DOING TESTS [CA]
10 A new promise but not a solution (6) ANSWER {A}{N}{SWEaR}
11 Run dog in park? (10) PLAYGROUND {RUN+DOG}* [RA]
12 Prized animal caught (4) DEAR (~deer)
13 According to the Reverend, bald assistant can keep locks in place? (8) HAIRBAND (~bare hand to hairband)
16 Relative accusing stationer's missing every now and then (6) AUNTIE {AccUsiNg+sTatIonErs}
17 Brown caught sweet model escaping (6) COFFEE {C}{tOFFEE}
19 Eggs, nuts, lentils and meat perhaps delivered for adolescents (8) PROTEINS {~pro teens}
21 Politically correct leaders were overwhelmingly knowledgeable. Extraordinary! (4) WOKE Acrostic
22 Celebrity on holiday forgets about hunger (10) STARVATION {STAR}{VAcaTION}
25 Skimpy elite insiders let off (6) LITTLE {eLITe}{LET*}
26 Soon time will change feelings (8) EMOTIONS*
27 That man's describing Bill in grand captions (8) HEADINGS {HE{AD}{IN}{G}S}
28 Cuts small fruits (6) SPEARS {S}{PEARS}
DOWN
2 Guide allowed to display model (5) IDEAL [T]
3 Want to cycle around end of forest and river opening (5) ENTRY {(-y)EN(+y)Y} over {f...sT}{R}
6 Girl managed naughty mad nana (7) GRANDMA {G}{RAN}{MAD*}
7 For a change, desire new, extremely comfortable house (9) RESIDENCE {DESIRE*}{N}{Co...lE}
8 First lady almost possessed by excitement is high (9) ELEVATION {EL{EVe}ATION}
14 Beg pardon! Associate Grace is maintaining journal (9) APOLOGISE {A}{PO{LOG}ISE}
15 Noted umpire chosen ignoring captain (9) REFLECTED {REF}{eLECTED}
18 Festival not at first Levantine (7) EASTERN {EASTER}{Not}
19 Appeals from contenders switching sides (7) PRAYERS P(-l+r)RAYERS
20 Unconcerned when a couple of Lilliputians go missing undisguised (7) O?V?O?S ()
23 Family involved in neonate birth's coming back (5) TRIBE [T<=]
24 Ultimately to somehow in the register, find titleholder (5) OWNER Tail Acrostic
Reference List
New = N, Caught = C, Model = T, About = CA, Bill = AD, Grand = G, Small = S, River = R, Girl = G, Associate = A, Sides = L,R



