Across:
   2. Dubious theories U.S.A. offered (3)
   8. Ill as a result of 11th letter as it was originally written previously (4)
   9. Trite city diplomacy and 26 10 after 9/11 and 16 4 helped it pass (7 3)
  10. Opinions expressed in 23, idealist or otherwise (10)
  11. Multitude in farmyard (4)
  12. Join a very loud team in pursuit of diamond (5)
  13. Rebuilt knees slot into such structures? (9)
  16,4dn. Nasty correspondence of worker with HR: a tax return and attachments (7 7)
  17. see 25 down
  20. Intent on Iraqi conflict, George finally falsely claimed ingredient in 16 4, framing 22 (9)
  22. Revolutionary angry while national leader? (5)
  24. A long way off, but Nadal is coming back! (4)
  26. Herb policy developed as a sort of tangent (10)
  27. Probable 16 4 culprit: 25 17 worker, and first to benefit with spoils on embracing nasty vice (5 5)
  28. Some may come from old school site when destroyed (4)
  29. 4 ostensibly represented cry for help (3)
Down:
   1. One seed FBI cultivated as response to 16 4 perhaps (10)
   2. Fickle, like satirical piece perhaps (8)
   3. Prose rewritten as something more infectious? (5)
   4. see 16 across
   5. Contributed to solution and damaged evil's odds (9)
   6. Artist recreated maritime passage (6)
   7. Computers turned to fraud (4)
  14. Fruit of cultivated trees in can? (10)
  15. Outdoor furniture's early promotion heard before broadcast (4 5)
  18. Concerned with one's misgivings, not having first of 27's displays (8)
  19. No love in stoic type mostly included to staunch bleeding (7)
  21. Mostly the staple meal, taken so often in a day? (6)
  23. Fleet street crowd? (5)
  25,17ac. Henry taking his popular model close to complete deception for U.S. 11 base, studying 1 (4 7)