PUZZLE 51

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Across
  1. 1. Queen Elizabeth II worked as one during World War II (8)
  2. 5. Popeye's nemesis (5)
  3. 7. Once used with candles to tell the time (5)
  4. 9. Collective name for a group of hippos (5)
  5. 11. Overwhelming defeat (4)
  6. 12. Invented by Frank Epperson in 1905 and known as a lolly in the UK (8)
  7. 13. Burdensome demand paid to the government (3)
  8. 14. Creatures immune to cancer (6)
  9. 16. Pig-like (7)
  10. 17. Scale-covered anteater (8)
  11. 18. 19th century opium tincture used as a painkiller (8)
  12. 20. Most-followed sport worldwide (6)
Down
  1. 2. Lack of respect (8)
  2. 3. Used by cats as a width guide (8)
  3. 4. A dog that never barks (7)
  4. 6. The only even prime number (3)
  5. 8. Tennis playing surface at Wimbledon (5)
  6. 10. Traditional roof material in Norway (4)
  7. 13. The nursery rhyme 'Ring-a-Roses' is about this disease (3,6)
  8. 15. The only food item that never spoils (5)
  9. 19. Young kangaroo or koala (4)