ACROSS
 1. <avoided> ESCHEWED = ESC HEWED
 6. ←BUS← DUE = SUBDUE <to cow>
 9. <checked> CURBED = B inside CRUDE*
10. APE IT IF outside R = APERITIF <alcoholic drink>
11. <President of France> MITTERRAND = MITT + ERRAND
12. <fancy> IDEA = IDE A_
13. (ANTHEM outside A_) A = ANATHEMA <pariah>
15. <workplace> OFFICE = (OFF ICE)
17. <whinge> SNIVEL = _N inside ←LEVIS←
19. <going> OUTBOUND = OUT-BOUND {jump better than}
21. <farm animals> EWES = "YEWS"
23. <debauchery> PERVERSION = PER VERSION
25. PLEA outside THOR = PLETHORA <abundance>
26. LAW inside FED = FLAWED <imperfect>
27. <made brown> SEARED = SEA + RED
28. LINGERIE - I + _D = LINGERED <stayed there>

DOWN
 2. <wine> SAUVIGNON = U inside S AVIGNON
 3. H (A BIT) AT = HABITAT <home>
 4. <bird> WADER = W A ←RED←
 5. (SOLDIER ON ADA ADA)* = DEAD AS A DOORNAIL <unmistakably deceased>
 6. S PEED + BOA T = SPEED-BOAT <vehicle>
 7. <court official> BAILIFF = FF after ALIBI*
 8. <join> UNITE = UNI T_ E_
14. ←(.a)DIO SPILLE(d.)← = ELLIPSOID <ball>
16. CAN TONES E_ = CANTONESE <Chinese language>
18. VI ←ROTIS← = VISITOR <guest>
20. <playing> ON STAGE = STAG inside ONE
22. LIED* after W = WILDE <writing Oscar>
24. (EL FIN) = ELFIN <fantastically charming>