Solving time, 19 mins, so not too difficult.
* = anagram < = reversed
ACROSS
1 NAT HAN(d) tan<
4 S (PORT) ING
9 B (EAR) OUT
11 UP P (SAL)A
12 SONS AND LOVERS DH Lawrence novel A N in (dross novels)*
14 B UTTER NUT
15 L ASS O
16 T (A R) OT
18 PER (MANE N)T N = latest in fashion (last letter)
20 ANCIENT LIGHTS (licensing that)* New to me, worked it out when I’d enough crossing letters – the right to light, I think.
23 TREACLE (celebrate)* less be
24 G L (OB) OSE miss = lose
25 DISPERSE (red spies)*
26 BE L FRY
DOWN
1 NO(B)S son (disciple) < My last answer.
2 TRANS(m)IT
3 A DO (RN MEN) T
5 POUND STERLING (got in plunders)*
6 REP (material) RO(t)
7 IN A MESS ie I NAME SS !
8 G RA (SS) ROOTS (orators)*
10 TRAIN (school vb) S POTTERS
13 ABSTR ACTED (brats)*
15 LOATHSOME (a note most)*
17 (c)RICKETS Good misleading surface.
19 plEASE OFFer some outside letters (in a regular pattern) go.
21 servicE M (CE) E
22 LEV(it)Y