Across:
   1. Secure behind border plant (7)
   5. Splendid chap, one talking away with his leader and 4 (7)
   9. The west, for 21, is in a mess (5)
  10. In theory, no shopping centre allowed in cooperating country (9)
  11. Primate with revolutionary sex tips (6)
  12. see 18dn
  13. Steven singing with President X (5)
  15. Leaving as planned, with less of "adieu" than as I arrived? (10)
  17. Time one's workout (3)
  20. 11ss? (10)
  22. Part of family confused without a 4 (5)
  24. see 18dn
  25. Local city neighbourhood (6)
  28. Exposure of limits in openers' talent (9)
  29. Extracted reported object (5)
  30,19,7dn. After 7, 4's letters banal: this U.S. line! (7 3 5)
  31. Crap time in crappy place (7)
Down:
   1. 22 of 18 controls second article (6)
   2. Human one essentially mostly horse's body without a brain (9)
   3. Twist 4 away from branch offering peace (5)
   4. Mother leaves construction boss (4)
   5. Party people, in company with single woman inhabiting another world (10)
   6. "Pepper Stew" act tune up (9)
   7,19ac,18. After 18, 4's retro dance venue superficially used to prohibit one dance, but had a time to slip one in (5 3 8)
   8. Hacking angrily with end of knife - one way to cut hair! (8)
  14. One in next consumed by a tiny negative thing - an inclusive measure? (10)
  16. Trimming of cloth as hem - it ends with a 4 of 21 perhaps (9)
  17. Hanging in final stage... ultimately you wear a thin ironic smile (9)
  18,12ac,19ac,24ac,30ac. After 30, 4's first two letters boring - a greeting one can mostly half-comically use in embracing such leader (8 2 3 2-7)
  21. River country (6)
  23. Mobs left in jails (5)
  26. Morning person? 5 across! (5)
  27. Tainted when passed by word of mouth (4)