Solving time, 15 mins, so fairly easy.
* = anagram
ACROSS
1/12 CALL OF THE WILD Book by the American writer Jack London
4 CU TS OUT Cu = Copper (stout)*
9 ROUGH-HEWN (How hunger)*
10 TA (Territorial Army) TA (thanks) R (king). I think the ‘warrior’ definition may go back to the time of Genghis Khan, though nowadays I think they are just a race, like many others.
11 MA (CHE) TE
13 STEAL THE SHOW (He’s Welsh OTT)*
17 CONS PIRAT (OR) S pirates less E or = gold
20 DEEJAYS Disc jockey/dinner jacket
21 OF FENCE
23 MIA MI(a)
24 REASON OUT which could indicate ‘a snore’ (as an anagram)
25 ART IS T (beginning to transmit) E (energy)
26 SK (1 MP) Y
DOWN
1 CH ROME (more)* My favourite clue “Church needs more chucked in the plate”
2 LA (UN) CE
3 OCH RE
4 CONSTITUTIONAL Double definition
5 TO T HE R EAR
6 OUT RIGHT
7 TURN DOWN
8 F EDERAL (dealer)* RESERVE (book) From the US
14 TOPI ARIES
15 ACADEMIA (Medic AAA)*
16 UNDERACT (true cad n)*
18 IN FORM
19 Bobbie GENTRY Singer, best known for “Ode to Billie Joe” (1967)
22 FROCK R (right) for L (left) in FLOCK