PETO kicks off the week…
An enjoyable puzzle with some lovely clues and nothing too troubling. I do wonder if I've got 1a right though, as it feels like there might be other valid answers (not that I can think of them however).
Thanks PETO!

ACROSS
1. Begins with exclusive groups at university (4,2)
SETS UP
SETS (exclusive groups) + UP (at university)
5. Mark with a tick by name of playwright reportedly (5,3)
CHECK OFF
"Chekhov" (name of playwright, Anton Chekhov, "reportedly")
9. Bill tucking into brownish-red biscuit (8)
MACAROON
AC (bill) tucking into MAROON (brownish-red)
10. Complete with e-books on anger (6)
ENTIRE
E + NT (books) on IRE (anger)
11. Contributing to battle ended by former PM (6)
ATTLEE
[b]ATTLE E[nded] (contributing to)
12. Crack is ultimately daft for a writer like Lamb (8)
ESSAYIST
ESSAY (crack, attempt) + IS + [daf]T (ultimately)
Charles Lamb
14. Crazy nun and red-hot deb dancing (5,3,4)
ROUND THE BEND
(NUN and RED HOT DEB)* (*dancing)
18. Overcoat, fleece and shirt destroyed by duke (12)
CHESTERFIELD
(FLEECE and SHIRT)* (*destroyed) by D (duke)
22. Jazz fan speaking with fellow from the French capital perhaps (8)
KATMANDU
"cat" (jazz fan, "speaking") with MAN (fellow) + DU (from, French)
25. Deny getting information about speed right away (6)
NEGATE
(GEN)< (information, <about) + [r]ATE (speed, R (right) away)
26. Unable to find a denial in pious platitudes (6)
CANNOT
NO (a denial) in CANT (pious platitudes)
27. Command at the end ignored by soldiers of Mussolini, for instance (8)
DICTATOR
DICTAT[e] (command, at the end ignored) by OR (soldiers)
28. He makes insistent demands with criticism Lear’s answer dismissed (8)
STICKLER
STICK (criticism) + LE[a]R (A (answer) dismissed)
29. Practises a form of singing? Yes old style (6)
YODELS
DOWN
2. Insists upon finding old deeds (6)
EXACTS
3. Modest heraldic insignia featuring pistols for example (5-4)
SMALL-ARMS
SMALL (modest) + ARMS (heraldic insignia)
4. Practise with Sue (9)
PROSECUTE
5. Conservative aim? To embrace the start of tussle in opposition (7)
CONTEND
(CON (conservative) + END (aim)) to embrace T[ussle] (start of)
6. Just before son quits (5)
EVENS
EVEN (just) before S (son)
7. Communal fund for equipment supported by both sides in theory (5)
KITTY
KIT (equipment) supported by T[heor]Y (both sides)
8. Cheap sarong readjusted by dandy endlessly (3,1,4)
FOR A SONG
(SARONG)* (*readjusted) by FO[p] (dandy, endlessly)
13. Helping to make scapegoat of mimic (3)
APE
[sc]APE[goat] (helping to make)
15. Henry about to stop — surprisingly unready for pursuit of suspect (3,3,3)
HUE AND CRY
H (henry) + (C (about) to stop (UNREADY)* (*surprisingly))
16. Bad guy Rod played in Minder (9)
BODYGUARD
17. Old agricultural labourer carrying home game bird (8)
PHEASANT
PEASANT (old agricultural labourer) carrying H (home)
19. Drink providing limitless energy (3)
TEA
[s]TEA[m] (energy, limitless)
20. Discovered on oddly neglected retro sink (7)
FOUNDER
FOUND (discovered) on [r]E[t]R[o] (oddly neglected)
21. Easy victory seconds before offensive online post (6)
STROLL
S (seconds) before TROLL (offensive online post)
23. Frantically busy soldier in charge (5)
MANIC
MAN (soldier) + IC (in charge)
24. Not available to speak about falling short in former South African province (5)
NATAL
NA (not available) + TAL[k] (speak about, falling short)
Your solution and parsing to 1A seems fine to me, Teacow. The entry for “set up” in Chambers has “begin” as one of its meanings.
Found this an enjoyable 21d. 1a is how I parsed it too.
Favourite things were the ‘criticism’ for ‘stick’, ‘essay’ for ‘crack’, KATMANDU and HUE AND CRY.
Knew it was TEA but for the life of me, I couldn’t conjure ‘steam’.
Thanks to Peto and Teacow.
Thanks Peto and Teacow
25ac: I am sure that the indication for DU is meant to be “from the” (French). That is certainly valid, and I have considerable doubts over the possible validity of translating “DU” on its own as “from”. I am prepared to be corrected by a later edition, but my 1996 copy of Larousse shows du in a table headed Articles at the beginnings of the dictionary. The word du appears only in the first column, headed article défini (along with de la, de l’, and des): du does not appear in the third column headed absence d’article (where de can be found).
Comment 3 of course refers to 22ac, not 25ac.
You’re right, Pelham. ‘De’ is ‘of’ or ‘from’ before adding any of the definite articles you mention to make ‘from the’ or even ‘some’, eg. voulez-vous du vin?
I got EVENS OK from the wordplay, but I do not understand how that is equivalent to “quits”? I saw some dictionary entries for both words relating to canceling debts, but if that is the common element, that usage is not familiar to me.
Cineraria@6
We’re quits/we’re even/we’re square -I have come across these usages in the same sense.
Might have originated from the context you mention.
Cineraria: how about “double or quits”? Similarly “quitting up” is a way of evening things up between people.
SETS UP:
Teacow’s parsing seems all right to me (as Rudolf and Diane have mentioned here). Maybe the def is ‘begins’ instead of ‘begins with’? ‘With’ could be a link word.
Thanks to P and T!
Thanks for the blog , a neat set of clues , ROUND THE BEND is very funny, HUE AND CRY is a lesser known Ealing comedy with Alastair Sim
Thanks Peto. Except for my failure with PROSECUTE this went in easily even though I didn’t understand crack for essay, EVENS for quits, HUE AND CRY for pursuit of suspect, or where TEA came from. Favourite was CHECK OFF. Thanks Teacow for explaining it all.
In French ‘du’, is masculine, “de la’ is the feminine equivalent, so, du vin, but de la mer.
Kathmandu is the correct spelling
Dave @13: Kathmandu is correct but the word “perhaps” following “capital” may suggest that KATMANDU is an alternative spelling. Maybe the word “once” following “capital” would be more accurate.
Kathmandu is misspelt as Katmandu.
I’ve been there twice with a 45 year gap. Much more interesting the first time.
Very straightforward puzzle. Thank you for explaining a few mysteries.
I thought a Chesterfield was a fancy sofa. My mum called the long seat we sat on in front of the television as children the Chesterfield.
Delusions of poshness?
Apologies to 13 and 14 for making the same point about Kathmandu. I should’ve read these first
Katmandu/Kathmandu: Collins dictionary gives both alternatives
I’ve never seen it spelt “Katmandu” and none of the references I consulted spells it that way. But as nmsindy points out, Collins does. From my experience 99% of the time it’s spelt with an “h”.
I couldn’t parse 15d, and no wonder. Stop unready?
The only other one I failed to parse was DICTATOR … that pesky English OR again, that I’ve not seen for a while.
Otherwise pretty straightforward with a good number of smiles.
Why is “bill” “AC”?
bbbbbb@19: AC is an abbreviation for “account”. Watch out though: “bill” can also be AD(vertisement).
Geoff@18 re 15dn: “to stop” here is in the sense of “to obstruct” and means that the C is contained in an anagram of UNREADY.