ARTEXLEN kicks things off this week…
A very enjoyable solve this morning. I particularly liked 19a.
Thanks ARTEXLEN

ACROSS
1. Backing innocent against officer’s deception (5-2)
COVER UP
(PURE (innocent) + V (against) + OC (officer))< (backing)
5. Jointly endorse function in auditorium (6)
COSIGN
"cosine" (function, "in auditorium")
8. Suddenly giant turned on expert guards (3,2,4)
ALL AT ONCE
((TALL)< (giant, <turned) + ON), ACE (expert) guards
9. Keen to keep old duck (5)
AVOID
AVID (keen) to keep O (old)
11. Set down on soft cloth (5)
PLAID
LAID (set down) on P (soft)
12. Letter and formal deed about account (9)
CHARACTER
CHARTER (formal deed) about AC (account)
13. In disorder, cue riots and protests (8)
OUTCRIES
(CUE RIOTS)* (*in disorder)
15. Intervening, one succeeds for all to see in confusion (6)
MIDDLE
MUDDLE (confusion, I (one) succeeds U (for all to see, film rating))
17. Spring, not oddly, is a part available (6)
SPROUT
[i]S [a] P[a]R[t] (not oddly) + OUT (available)
19. Shared this, literally entertaining a French learner (8)
COMMUNAL
COMMA (this "," literally) entertaining UN (A, french) + L (learner)
22. Shunning all outsiders, simply pick matey associate (9)
IMPLICATE
[s]IMPL[y] [p]IC[k] [m]ATE[y] (shunning all outsiders)
23. Staff strike concerning (5)
BATON
BAT (strike) + ON (concerning)
24. Heating apparatus part of newest oven (5)
STOVE
[newe]ST OVE[n] (part of)
25. Garment unfortunately apt to clash primarily with tie (9)
PETTICOAT
(APT TO C[lash] (primarily) with TIE)* (*unfortunately)
26. Gems from abbey royals so regularly used (6)
BERYLS
[a]B[b]E[y] R[o]Y[a]L[s] S[o] (regularly used)
27. Clough’s wingers advanced on other team (7)
CHELSEA
C[loug]H (wingers) + (A (advanced) on ELSE (other))
DOWN
1. Husband entering plants joint with son for contests (13)
CHAMPIONSHIPS
H (husband) entering CAMPIONS (plants) + HIP (joint) with S (son)
2. Heroic victor over boxer, six-footer (7)
VALIANT
V (victor) over ALI (boxer) + ANT (six-footer)
3. Expensive climbing frames tons valued (5)
RATED
(DEAR)< ( expensive, <climbing) frames T (tons)
4. Thief interrupted by small dog (8)
PINSCHER
PINCHER (thief) interrupted by S (small)
5. He dictated what might precede salad (6)
CAESAR
6. Fellow is drawn into fake religion (9)
SHAMANISM
(MAN (FELLOW) + IS) drawn into SHAM (fake)
7. Broke all contact with good journalist protecting entertainer (7)
GHOSTED
(G (good) + ED (journalist)) protecting HOST (entertainer)
10. Drink in jar delegate’s drunk (10,3)
DARJEELING TEA
(IN JAR DELEGATES)* (*drunk)
14. Regularly decrypted your intel (9)
ROUTINELY
(YOUR INTEL)* (*decrypted)
16. Monk in Mont-Saint-Michel is in charge of dwelling-place (8)
DOMESTIC
DOM (monk) + EST (is, in Mont-Saint-Michel) + IC (in charge)
18. Criticise soldiers for case of vengeance (7)
REPROVE
RE (soldiers) + PRO (for) + V[engeanc]E (case of)
20. Concepts central characters in Pentagon dismissed in writings (7)
NOTIONS
NOT[at]IONS (writings, [pen]TA[gon] (central characters in) dismissed)
21. Mike cutting father’s grass (6)
PAMPAS
M (Mike) cutting PAPAS (fathers)
23. Informed of spaces for loading surface material (5)
BAIZE
"bays" (spaces for loading, "informed of")
Very easy with a few clues needing a bit of thought.
20a should be NO[ta]tions.
A perfect Monday solve with just one interesting little wrinkle at 11a.
Initially, I had entered PLACE (set down) on soft, P, + LACE (cloth), which almost worked but was soon ironed out RATED.
So, of course, the true definition was found at the other end of the clue, with its alternative workings.
Plain sailing other than this.
Favouites were the dog (4d), club (27a) and tea (10d)
Thanks to Artexlen and Teacow.
Good fun, with nothing too taxing. I’ve learnt a lot of British things from doing these and the Guardian’s crosswords, but alas not the hierarchy of film classifications, so I failed to solve MIDDLE. My favourite was COMMUNAL.
Thanks, Artexlen and Teacow!
Enjoyed the puzzle and the blog!
COMMUNAL: Liked it very much.
Thanks Artexlen and Teacow
11ac (PLAID): I had the same issue as Diana@2. I would go as far as to say that the clue is completely ambiguous in isolation. However, it is the sort of ambiguity which I am ready to forgive.
Me too, Pelham, as it was perhaps purely coincidental.
Good fun. I am another fan of COMMUNAL. There is no s in the fodder for Darjeeling Tea.
Thanks for the blog, good set of clues , neat, precise and concise.
I think that PLAID is a slight favourite for 11Ac being an actual cloth but I can see both. It is quite rare for clues to give two plausible answers in different ways.
Thanks Artexlen for a good start to the week. I too initially had PLACE instead of PLAID but, like Diane, RATED had me rethink the clue. I never solved BAIZE and I couldn’t parse NOTIONS but all else was smooth sailing. My top picks were COSIGN, AVOID, MIDDLE, VALIANT, PINSCHER, and GHOSTED. Thanks Teacow for the blog.
We too went for ‘place’ initially but soon realised our mistake. With less justification we went for ‘cosine’ partly because we would enumerate CO-SIGN as 2-4, but as it’s not in Chambers or Collins we can’t verify it (although ‘cosignatory’ isn’t hyphenated). We did realise our error eventually to get GHOSTED. We did, though, spot the need to spell out the punctation to get COMMUNAL.
A pleasant and not too taxing solve. Thanks, Artexlen and Teacow.
I too went for place but never changed, so couldn’t get “rated”.
This was not easy for me but I got most of it. Perhaps it’s just me, but on 17a, when we are “out” of something, it’s not available. So I felt very stumped on that for a long time.
Anil @12: “The author’s new book just came out” is akin to “the author’s new book just became available.”