ARTEXLEN kicks off the week…
A mostly straightforward puzzle, though I’d not come across 25a before, so that took me a while.
Thanks ARTEXLEN!

ACROSS
1. Man painting Ben, legendary figure (4,6)
KING ARTHUR
KING (man) + ART (painting) + HUR (Ben)
7. Quietly feeding timid parrot (4)
COPY
P (quietly) feeding COY (timid)
9. Content to canter after turning mount (4)
ETNA
([c]ANTE[r] (content to))< (<after turning)
10. Insect, beast native to Africa, crossing river to get home (10)
MOTHERLAND
MOTH (insect) + (ELAND (beast native to Africa) crossing R (river))
11. Fantastic runner led all regularly (6)
UNREAL
[r]U[n]N[e]R [l]E[d] A[l]L (regularly)
12. Flattered being lauded at swimming (8)
ADULATED
13. Characters arrested by coppers on aeroplane (8)
PERSONAE
[cop]PERS ON AE[roplane] (arrested by)
15. Location is place interesting to tourist, we’re told (4)
SITE
“sight” = SITE (place interesting to tourist, “we’re told”)
17. Work with aluminium and stone (4)
OPAL
OP (work) with AL (aluminium)
19. Supports pre-eminent player in rounders (8)
BACKSTOP
BACKS (supports) + TOP (pre-eminent)
22. Add more detail to vegan maxim? (5,3)
FLESH OUT
Double (cryptic) definition
23. Pretty lady’s after scoundrel (6)
RATHER
HER (lady) after RAT (scoundrel)
25. Initially confused when American with paunch announced reason for war (5,5)
CASUS BELLI
C[onfused] (initially) + AS (when) + US (American) with “belly” = BELLI (paunch, “announced”)
26. Pop group from estate disregarded in part of London (4)
WHAM
W[est] HAM (part of London, EST (estate) disregarded)
27. Extremely cagey reviewer holds back (4)
VERY
([cage]Y REV[iewer])< (holds, <back)
28. Floral collection one regards untidy (4,6)
ROSE GARDEN
DOWN
2. Great in numbers, Everton’s lead (7)
INTENSE
IN + TENS (numbers) + E[verton] (lead)
3. Mark became dull in speech (5)
GRADE
“greyed” = GRADE (became dull, “in speech”)
4. Queen on stroll talking at length (8)
RAMBLING
R (queen) + AMBLING (on stroll)
5. What better tools to forge bed- warming devices? (3-5,7)
HOT-WATER BOTTLES
(WHAT BETTER TOOLS)* (*to forge)
6. Sorry French road endlessly congested (6)
RUEFUL
RUE (French road) + FUL[l] (congested, endlessly)
7. Colonel drinks establishments empty and keels over (9)
COLLAPSES
COL (colonel) + LAPS (drinks) + E[stablishment]S (empty)
8. Joke with fellow that’s sharp (7)
PUNGENT
PUN (joke) with GENT (fellow)
14. Speak about city in Northern Ireland briefly — cathedral city (9)
SALISBURY
SAY (speak) about LISBUR[n] (city in Northern Ireland, briefly)
16. Deriding Carol, say, keeping company with sailors (8)
SCORNING
SING (carol, say) keeping (CO (company) with RN (sailors))
18. Raid shelled small settlements with superior power (7)
PILLAGE
[v]ILLAGE[s] (small settlements, shelled) with superior P (power)
20. Go over school subject with class (7)
OPERATE
O (over) + PE (school subject) with RATE (class)
21. Car accessory is to deform road surface, according to Spooner (3,3)
TOW BAR
“bow tar” (deform road surface, “according to Spooner”)
24. Tall building to west engineers erected (5)
TOWER
TO + W (west) + (RE)< (engineers, <erected)
Or GRAZE for 3D?
I must admit I put in GRAZE reading the clue as ‘becomes dull’ for some reason. Mostly straightforward. Hadn’t met CASUS BELLI but easy to guess. Not keen on 1a. Feel it works better if it was BEN HUR, rather than BEN-HUR.
I parsed KING ARTHUR incorrectly as KING = man and then ARTHUR as ‘Ben Arthur’ (mountain in Scotland) thereby ignoring the word ‘painting’ – must pay more attention to detail instead of jumping too quickly to enter a solution that just seems correct.
Otherwise all good fun.
Thank you Artexlen and Teacow.