PETO kicks off the week…
An enjoyable and reasonably straightforward puzzle, though I’d not come across 18d and 19a before.
Thanks PETO!

ACROSS
1. Alcohol induced confidence of crude gaucho developed over time (5,7)
DUTCH COURAGE
(CRUDE GAUCHO)* (*developed) over T (time)
8. Plant evidence finally after trap brought about return of American students (7)
NIGELLA
([evidenc]E (finally) after (GIN)< (trap, <brought about)) + (A (American) + LL (students))< (<return of)
9. Agreed to get high-backed bench then died (7)
SETTLED
SETTLE (high-backed bench) then D (died)
11. On which to post new source of tittle-tattle without delay (7)
INSTANT
INSTA (on which to post) + N (new) + T[ittle-tatle] (source of)
12. Polish needed on fellow’s shoes (7)
SANDALS
SAND (polish) needed on AL’S (fellow’s)
13. Get rid of English class system (5)
CASTE
CAST (get rid of) + E (English)
14. Letter showing account including hire of transport? Just the opposite (9)
CHARACTER
AC (account) including CHARTER (hire of transport), just the opposite
16. Crude oil painting initially has part to play in dumb show actor’s withdrawal (9)
PETROLEUM
P[ainting] (initially) has (ROLE (part to play) in (MUTE)< (dumb show actor, <withdrawal))
19. Introduction of energy during concert (5)
PROEM
E (energy) during PROM (concert)
21. Hellenic people rebuilding on Sinai (7)
IONIANS
(ON SINAI)* (*rebuilding)
23. Argue against portent and commit forever (7)
CONSIGN
CON (argue against) + SIGN (portent)
24. Plead for space to have free entertainment (7)
ENTREAT
EN (space) to have TREAT (free entertainment)
25. Burn most of letter revealing sweet conveyance of rugby anthem (7)
CHARIOT
CHAR (burn) + IOT[a] (letter, most of)
26. Wear perfume to meet soldiers in recreation facility (6,6)
SPORTS CENTRE
SPORT (wear) + SCENT (perfume) to meet RE (soldiers)
DOWN
1. Mentally assimilates abstract poems at last (7)
DIGESTS
DIGEST (abstract) + [poem]S (at last)
2. Mounting bitterness hindering restraint in husbandry (7)
TILLAGE
(GALL)< (bitterness, <mounting) hindering TIE (restraint)
3. Heather upset over Bill’s anguish (9)
HEARTACHE
(HEATHER)* (*upset) over AC (bill)
4. Drives out in posh street in the middle of Crosby (5)
OUSTS
(U (posh) + ST (street)) in [cr]OS[by] (the middle of)
5. Plump architect’s principal round building (7)
ROTUNDA
ROTUND (plump) + A[rchitect] (principal)
6. Girl left social worker for dashing young man (7)
GALLANT
GAL (girl) + L (left) + ANT (social worker)
7. Lack of self-control in popular apostle concerned with interrupting (12)
INDISCIPLINE
IN (popular) + (DISCIPLE (apostle), IN (concerned with) interrupting)
10. Record speed over a short time to note differences (12)
DISCRIMINATE
DISC (record) + (RATE (speed) over I MIN (a short time))
15. Cram case designed to carry earliest of handguns into weapons store (4,5)
ARMS CACHE
(CRAM CASE)* (*designed) to carry H[andguns] (earliest of)
17. Lose against leading pole jumper (4,3)
TANK TOP
TANK TO (lose against) + P[ole] (leading)
18. Derelict area not enjoying spell of great success (2,1,4)
ON A TEAR
19. Identifying flag of old queen upraised by knight in port (7)
PENNANT
((ANNE)< (old queen, <upraised) by N (knight)) in PT (port)
20. Opening with soldiers assuming that coldness of manner (7)
ORIFICE
OR (soldiers) + IF (assuming that) + ICE (coldness of manner)
22. Locates spectacles reportedly (5)
SITES
“sights” = SITES (spectacles, “reportedly”)
I struggled with a good percentage of this. Never heard of the high-backed bench, nor PROEM. I couldn’t figure out treat/”free entertainment” and in/”concerned with”.
I also couldn’t get “in = concerned with”
Top half went in quickly but struggled a bit in the SE
Liked: NIGELLA, GALLANT, SPORTS CENTRE, DISCRIMINATE
Thanks Peto and Teacow
Ditto Teacow and GDU re proem; etymoloy not obscure, just rarely used I guess. Otoh, have met On a tear, though On a roll is more usual here. Being more or less e-antisocial, didn’t twig insta so instant was a bung. Pleasant enough potter, ta Peto and Teacow.
A good puzzle to ease me back into my daily cryptic habit. What a help DUTCH COURAGE turned out to be. Just PROEM was unknown but parsing and crossers came to the rescue.
Thanks to Peto and Teacow.
Thanks Peto and Teacow
24ac: Chambers 2016 (p 1662) has “a free entertainment, pleasure excursion or feast” as its first definition of treat as a noun. Collins 2023 (p 2100) has much the same thing in different words: “a celebration, entertainment, gift, or feast given for or to someone and paid for by another”.
17dn: Both Chambers (p 767) and Collins (p 986) have “concerned or involved with” among the meanings of in as a preposition. Collins gives in journalism as a usage example.
managed to finish it despite never having heard of PROEM either.
liked 17D
I’m among those who dislike “leading pole” to clue P, so that one (TANK TOP) was my least favorite and last in. Yes, a P is leading the word pole, but that does not make “leading pole” mean P.
I had in fact seen the word PROEM before, so that one didn’t hold me up.
Likewise I had heard of PROEM because I think it came up in an Azed not long ago. I vaguely remember seeing the word in capitals on the first page of books of long and dreary eighteenth century verse, but was never tempted by the proem to read them.
Had never heard of ON A TEAR and also had to assume INSTANT was correct because I too had never heard of INSTA. I surmise it has something to do with Instagram.
I’ve heard ON A TEAR – sports commentary for that version. Also Insta for Instagram, from people who use it a lot
Thank you to Peto and Teacow
11ac/18dn: Further to Shanne@9, both insta and on a tear can be found in Collins 2023, defined respectively as “informal the photo-sharing application Instagram” (p 1009) and “slang showing a sudden burst of energy” (p 2028 under the headword tear²). I could not find either in Chambers 2016, although Instagram in full is on p 789 under the headword insta- and marked as a registered trade mark.
17dn: I share the misgivings expressed by mrpenney@7 about the use of “leading pole”.
I also struggled with the south east. What with PROEM being the header there and not remember you spell CENTER as CENTRE! Also took me a long time to get 2D. But I live in downtown New York city, so with my living location, I could get village (east or west or Greenwhich) or perhaps even pillage which is long standing activity by New Yorkers of all sorts on Manhattan but hardly any TILLAGE around here.
I enjoyed this and it flew in by my standards
Enjoyed most of this but ‘crude oil’=PETROLEUM? Not in my world.
Thanks both.
16ac: For crude oil, we have the following:
“petroleum before it has been refined” in Collins 2023 p 483;
“petroleum in its unrefined state” in Chambers 2016 p 372;
“(an) unrefined petroleum” in the Shorter Oxford English Dictionary 2007 p 570.
I suspect Peto uses Collins as the main reference – see comment 10 for my reasons for this – but I will take any one of these as a fair representation of standard UK English, which is the language of the FT crosswords, as is clear from the spelling of the answer at 26ac.
What’s the relevance of “just the opposite” in the 14a clue?
14ac: The answer is formed as AC inserted into (or included in) CHARTER, so it is the opposite process from AC including CHARTER, which would give ACHARTERC. Roger@15, I hope that helps. Setters sometimes do this sort of thing when the opposite of the wordplay required gives a more natural surface to the clue.
Thank you Pelham @16, that makes sense to me now.