ACROSS
 9. <show> OSTENTATION = (NINE TATTOOS)*
10. <a singular> ONE = O NE
11. <aristocrat> NOBLE = TA out of NOTABLE
12. <red> SOCIALIST = CIALIS inside SOT
13. <directors> COXSWAINS = CO + XS WINS outside A_
16. _E + LITE = ELITE
17. C ON TRAIN DI CAN'T S_ = CONTRAINDICANTS <reasons not to proceed>
19. <bike> MOPED <was blue>
21. GUISES* DUP = GUSSIED UP <given a makeover?>
23. <paid off> AMORTISED = MEDIATORS*
25. <Python worker perhaps> CODER = "CODA"
27. _D_ _I_ _E_ = DIE <perish>
28. <jacket accessory> SHOULDER PAD = SHOULD DRAPE*

DOWN
 1. <drink> COGNAC = ←CAN GO C←
 2. <go> STAB = ←BATS←
 3. TRAINER* outside W = INTERWAR <between fights>
 4. (WAS SAILING) = WASSAILING <singing tradiitonal songs>
 5. _Z INC = ZINC <heavy metal>
 6. <I'm doing porridge> INMATE = IN MATE
 7. <did place> POSITIONED = ←(.a)DE NO IT IS OP(e.)←
 8. <moving> RESTLESS = (.t)RESTLE'S S(t.)
14. <they hate those foreign> XENOPHOBES = (PHONE BOXES)*
15. SIDES ADDLE = SIDESADDLE <horse-riding strategy>
17. <having not donned pants> COMMANDO = COMMA DON*
18. N inside CLICHE _R = CLINCHER <coup de grâce>
20. <hate> DETEST = (D E) + TEST
22. <send up> PARODY = ROD inside PAY
24. <leave> SHOO = SHOO[-t]
26. <use performance-enhancing drugs> DOPE = (DO PE)