Solution to 26A 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 Possible to say, trade in scrap (6) CANCEL {CAN}{(~sell)CEL)
10 Complain about broken locks? (5,5) SPLIT HAIRS {SPLIT}{HAIRS}
11 Associate litigation relating to a court (6) ATRIAL {A}{TRIAL}
12 Spooner's bag hit chair behind the driver (4,4) BACK SEAT (Sack beat to back seat)
13 Agatha Christie novels and plays with sound (9) WHODUNITS*
15 Basically headgear - also topis sometimes (4) HATS Acrostic &lit
17 Herb's running after terrible game (9) BADMINTON {MINT}{ON}<=>{BAD}
22 Country dividing drug and alcohol (6) UGANDA [T]
24 Charming food shop's extremely garish bar's nearly crowded (10) DELIGHTFUL {DELI}{Ga..sH}{T}{FULl}
25 Has topless dresses (4) OWNS gOWNS
26 Without consuming drugs, model's most balanced (6) S?N?S? (Addendum - SANEST {SAN{E}S}{T} - See comments)
27 Peacekeeper's soldiers taking a line that's imaginary (6) UNREAL {UN}{RE}{A}{L}
DOWN
1 Spotted cat that's reportedly a rogue (7) CHEETAH (~cheater)
3 Reverse speech impediment in time for character in Greece (7) EPSILON {E{LISP<=}ON}
6 Snake was pickled in can for sailor (9) BOATSWAIN {BOA}{T{WAS*}IN}
7 Frequently use that in really round ropes (7) LARIATS {uSe+ThAt+In+ReAlLy}<=
8 Anything goes in Easter ball (3,4,3,3) ALL BETS ARE OFF {EASTER+BALL}* [RA]
14 Registered ardent interest primarily in rare and ethnic group (9) DRAVIDIAN {R}{AVID}{In...t} in {AND}*
16 Merchants following Government's rule score unexpectedly (7) GROCERS {G}{R}{SCORE}*
19 Spoken without sound for a second, say (7) ORDINAL {OR{DIN}AL}
23 Chiefly aloft, beyond or vertically elevated! (5) ABOVE Acrostic & lit
Reference List
Associate = A, Hard = H, Over = O, Bar = T, Drug = E, Model = T, Soldier = RE(Royal Engineers), Line = L, Uniform = U, Registered = R, Interest = I, Government = G, Rule = R

