Across:
   8. It may involve digging around evenly below remnants of holy crag (10)
   9,26. 19 who called the 12 17 4 and then put in his order (4 3 5)
  10. Give advance notice of reversal with pay cut by third of June (8)
  11. Beliefs can be barriers in courts - heart must be ignored (6)
  12. Starting trouble? It mostly comes back! (5)
  13. 8 field work pressed on, having lost lead and gone off track (9)
  15. Dominance expressed in "Dear Mother" (7)
  17. 3 16 HQ, one surrounded by vessels (7)
  20. Warning about beginnings of sexual affairs, and how one thing leads to another (9)
  22. Some shun it, yet all work together in it (5)
  24. Father's sister, contact in old leadership (6)
  26. see 9
  27. Use aluminium wrap for lack of leaks (4)
  28. In core of novel bill (a foil from the right), 12 17 4 claimed that 19 can be this! (10)
Down:
   1. Less smooth, but more hip? (8)
   2. Passionate celebration of Trinity sees Mother put out (10)
   3. Their figures may combine to be mild, civil, dim or vivid ... classically urban! (5)
   4. Incomplete tally (101-50) on the board (7)
   5. Lost student ruined hairstyle in panic (8)
   6. Drive some spirits up? (4)
   7. Fresh lust in man's push (6)
  14. Based on the evidence of smell about one, I fancy it's Columbian heads (10)
  16. "Universal" cast a chic lot (8)
  18. Shrewdly stay active around lute playing (8)
  19. Top man in 17: if fit, no player can hold him up (7)
  21. Ambushed, destroying initial ideas of 'married' and 'husband'? (6)
  23. Genuine major league! (5)
  25. Group with odd beliefs tailored to accommodate lustful leader (4)