Across:
   1. see 9
   4. Being cheeky, rubs the wrong way and upsets (8)
   8. Somewhere to sit and charm snakes with song (8)
   9,1. In France, my father interrupts his post: second prime minister and Polish-born president (6 5)
  10. Some thank Will, I am sure, being a musical legend (4 8)
  12. Terrible delay around opening of dam was fatal (6)
  14. Paper yields to them, as they are overcome by rock? (8)
  15. see 26
  18. Sets up to divide four fifths of twelve dozen? (6)
  20. see 2 down
  23,4dn. Sports star eager to use I.R. to get extra benefits... involving pub mostly! (6 7)
  24. My son's confused about big Apple words meaning the same thing (8)
  25. Curs sent running for cakes (8)
  26,15. Undefeated thrower of punches - a solid one reversed my trajectory before I got to one round! (5 8)
Down:
   1. Worked up about being well behaved (4)
   2,20ac. Unusually caring duo: heartthrob actor and acclaimed director (7 12)
   3. Talks about dog (5)
   4. see 23 across
   5. Sorting out love's awkward in a combative space (9)
   6. Facilities found in Turin also (7)
   7. Some OS parts to obtain when getting "up"? (10)
  11. Hanoi tax alert: some taken back for purpose of holiday? (10)
  13. Your first income, delivering heartfelt desires! (9)
  16. Career working around functions essentially? (7)
  17. Boost is arranged for musicians (7)
  19. Natural to be racing around after ball (7)
  21. Show nerve holding on to the one in possession (5)
  22. Salem mystery delivers award for drama writer perhaps? (4)