A prize awaits if you can solve x

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Across
  1. 1. Fishy treat reserved only for princes
  2. 3. Reacting to a faster way down
  3. 4. Indicator of emotional state, perhaps spun from straw
  4. 7. Essential resource
  5. 9. An inspiration to us all
  6. 11. The study and treatment of tumours
  7. 13. We are due for a rematch
  8. 14. A challenge for you
  9. 16. Holiday eating habits
  10. 17. Misleading transport to and from oxford
  11. 19. Do it
  12. 20. Site of many overhearings
  13. 21. Branch of natural science
Down
  1. 1. Something to fill from a mispelled tap
  2. 2. Seaside resort
  3. 5. Forename of a musical car
  4. 6. Butcher frequented by us
  5. 8. Favourite float
  6. 9. Contents of a prince's favourite course
  7. 10. We went here on holiday
  8. 12. Horrid wine
  9. 15. Deep rooted and kissed by fire
  10. 18. Man in uniform