Although not presented in the traditional "jigsaw" format, this is an "alphabetic" puzzle, in the sense that there is exactly one answer starting with each letter of the alphabet. If you'd like the jigsaw version, it is here.

Across:
   7,23dn. French poster for 2 down writer (6 6)
   8. see 21 down
  10. Six balls delivered, which is excessive (8)
  11. Frank, badly tired, scored century (6)
  12. Ray, who built big chain of knotted rope over canyon originally (4)
  13. 2 down state mouthpiece despises theocratic empires (10)
  15. Army man directed new 9 down (7)
  17. Some kerosene mixtures returned, as he was a great one for setting rules! (7)
  20. Most likely to have a start and get his lift into new organisation (10)
  22. Start of end of Raj by game administrator (4)
  24. Legend has New Zealand storms being caused by butterflies, according to his chaotic ideas (6)
  26. One of Washington's neighbours (new ones) (8)
  27. Young member of party blindly stabbing at rump of Democrat beast? (8)
  28. Country with some values we'd enjoy (6)
Down:
   1. Vietnamese president defeating 2 down president? (6)
   2. Quiet one was produced by green, as reported mysteriously in camera (8)
   3. Casual worker chasing coin is upset about union (10)
   4. Most of union's traditionally trained leaders rely on manipulation (7)
   5. Dog, if upset, quickly starts back to pound  (4)
   6. Badly rate "pain in neck" parts (8)
   9. Some swam Rubicon, returning to free country from 75 years back (5)
  14. Before fast movement, lead isn't commonly split, but it can add colour (10)
  16. Not as brave when odds are down? By real blood we earn! (8)
  18. Urged Joe, in end, to change (8)
  19. You an I mostly opposed those who warp their frameworks (7)
  21,8ac. Girl pursuing urgent earth restoration involving bold leadership? (5 8)
  23. see 7 across
  25. Zany ultimatum likely upset leaders in kingdom invaded 145 years ago (4)