Across:
   5. Using nitrous oxide perhaps, he'd made crude incision (6)
   8. Flawed hero, common in older type of film (10)
   9. Powerless to tip men off (8)
  10. In House of Milan, older line rejected for newer style (6)
  11. Good and bad omen in this little fellow? (5)
  12. They usually involve circuits of circle, set circulating (9)
  15,18dn,4dn. With new chemistry on call, open up periodical, publishing from 1872 (7 7 7)
  16. see 23
  19. Outrageous scam: niche specialists who "fix" your car (9)
  21. Mickey taken for being his mate, as Donald so silly! (5)
  23,16. Publication (once "10 12 and 19") which became "15 18 4" and dramatically saved Crow land (5'1 7)
  24. Dead cute eccentric is knowledgeable (8)
  25. Ditching hitching? These days it could be a conscious thing (10)
  26. Soft Metal I get into... so silly mostly! (6)
Down:
   1. A fighter, Don confused (8)
   2. Poor Tom Thumb, stripped and beaten as he always says too much (10)
   3. Little Bo Peep's lost animals, lost helpers, lost hands (5)
   4. see 15 across
   5. With terrible grime, roll of dice for one directed to achieve sanitation (9)
   6. Bones in pierced mouths coming up regularly (6)
   7. Airborne products of 10 12 and 19 which are found on bagpipes (6)
  13. Outrageously bare? As lone, not outrageous at all! (10)
  14. Soft Metal amusing me is so silly (9)
  17. Upper face fine when massaged (8)
  18. see 15 across
  19. Male straying worse when they cut someone's grass (6)
  20. Longed to swap 2nd and 3rd cut (6)
  22. Condition of union: entering plus moving (5)