Each letter of the alphabet appears at least once at the end of the solutions to the clues, which are to be fitted in the grid jigsaw-wise wherever they will go.
X American SI<O(xford)/U(ni)>X
Z Alcatraz A/L<CAT/R(uns)>AZ(y)
Y next year N<EX/T(ramwa)Y>EAR
S oasis double def
L oxtail (f)OXTAIL
A ballista BALL/1ST/A
P average up AV(erage)/UP (rev)
V spiv VIPS (rev)
U perdu PER<D(anes>U
C melodic ranCID OL(d) EM(menthal)
F shrug off FIGURE OF SPEECH less E(nglish)/PIECE (anag)
V Tel Aviv VIVA LET (rev)
Q NASDAQ Q AND AS (anag)
O reach to TOE ARCH (anag)
D outward OUT + DRAW (rev)
T queasiest QUIET SEAS (anag)
Y meat curry TA(rev)/CUR in ME(r)RRY
S oxheads O/X/HE/ADS
K hard disk HAR<DD/IS>K [Doctor of Divinity]
M snowstorm MR/O/TS (Eliot)/WON/S(omething) (rev)
E oeuvre O(ld)/E(English)/U(ltra)V(iolet)/R(oyal)E(ngineers)
G hashtag HAS/H(otel)/TAG
W pillow P(risoner)<ILL>O(f)/W(ar)
B absorb ABS/OR/B(uttocks)
J hadj HAD/J [J comes after I(ndia)]
I Yemeni ENEMY 1 (anag)
H footpath oldisH TAP TOO Frail (hidden rev)
N dorsal fin FOR ISLAND (anag)
L small Sado/Masochism/ + ALL
S two ounces WE SOON CUT (anag) [American liquid measure]