ACROSS
 7. <corrupt> BASTARDISE = BASE outside TARDIS
 9. "DOUGH" = DOE <female deer>
11. ←NDA← AU SEAM = AD NAUSEAM <annoyingly often>
12. M out of CONDOM = CONDO <apartment>
13. <questions> PUMPS <light footwear>
14. <one twin-hulled> CATAMARAN = CAN outside A TAMAR
16. TROUPER* F + (NT after HE) Z_ A_ U_ = RUPERT OF HENTZAU <villain>
19. <made a case for> JUSTIFIED = JUST IF IED
20. CO RPS = CORPS <group of soldiers>
21. <mountain ash> ROWAN = NORWA_*
23. M A inside TO TILL O = TOMATILLO <Mexican fruit>
25. IN K = INK <tattoos>
26. TAR "DEGRADE" = TARDIGRADE <resilient invertebrate>

DOWN
 1. <great work> MAGNUM OPUS = MAGNUS outside (U + MO P)
 2. <no charge> FREE = FEE outside _R
 3. <description of odd couple> MISMATCHED = (CHEMIST + MAD)*
 4. <minions> HENCHMEN = HENCE N_ outside HM
 5. <Norse god> ODIN = [-r]ODIN
 6. ←NAME B← outside _O_ = BEMOAN <lament>
 8. <PM> TRUSS = TRUSTS - T_
10. <gem> JASPER = (.a)JA'S PER(i.)
14. <they sing> CHORISTERS = (THIS SCORE)* outside R_
15. <grooming implement> RAZOR BLADE = →"BLAZER RAID"←
17. REIGN + I _T _E = REIGNITE <fire again>
18. <result> UPSHOT = UPS + HOT
19. JERK IN = JERKIN <sleeveless jacket>
20. <provide food> CATER = C_A_T _E_R
22. WII outside K = WIKI <website>
24. "MALE" = MAIL <metal armour>