ACROSS
 1. <one virtuosic with piece> SHARPSHOOTER = S HARPS + HOOTER
 8. <row> NOISE = N OISE
 9. <cheerful> EXUBERANT = EX UBER ANT
11. <perhaps ben> MOUNTAIN = MOUNT AIN'[-t]
12. <vinegary> ACETIC = _S out of ASCETIC
14. <tree> TEAK = T_E _A_K
15. <drugs> MEDICATION = MEDIATION outside C
18. _PLE B CITIES* = PLEBISCITE <vote>
19. E + PIC = EPIC <a long story>
21. ←GLUE← outside O + _Y = EULOGY <funeral speech>
23. <intellectual> CEREBRAL = CEREAL outside BR
25. <corresponding> ANALOGOUS = AN US outside A LOGO
26. <intimidate> DAUNT = GRAND-AUNT - GRAN
27. PEN inside (NICE ENDED)* = INDEPENDENCE <freedom>

DOWN
 1. <fire> STIMULATE = T inside SIMULATE
 2. <Fury> ALECTO = A_ L_ E_ C_ T_ O_
 3. _P RESIDENCY = PRESIDENCY <his office>
 4. HONOUR - ON = HOUR <time>
 5. <put more paint on> OVERCOAT = (TO COVER A)*
 6. <bang on> EXACT = ←C inside TAXE_←
 7. "ON A MATTER, PEER" = ONOMATOPOEIA <use of appropriate-sounding words>
10. <quibble> TECHNICALITY = (CATTILY + NICHE)*
13. <upset> DISTRESSED = D (IS TRESSED)
16. IMPORT UNE = IMPORTUNE <badger>
17. <synthesised air> RINGTONE = NITROGEN*
20. D_ E_ ADEN = DEADEN <numb>
22. <determine> LEARN = L_ EARN
24. <a quantity> SOME = "SUM"