Jacqueline King known to her friends as Jax played Sylvia Noble in Doctor Who beginning with the 2006 Christmas special The Runaway Bride. During Series 4, she made several appearances as Sylvia and returned to the role in 2009 for the final David Tennant storyline, The End of Time.
She also voiced "Barbara" in the Big Finish Productions - Doctor Who Unbound story Deadline.
In March 2013, Jax once again partnered up with Bernard Cribbins in a Doctor Who edition of the game show "Pointless Celebrities". Not only did they win a "Pointless" trophy each, but they also won the jackpot of £2,500. While Bernard gave his half of the jackpot to Sparks, Jax gave her share to the Northumbrian Lifeboats which her father had once supported. She also stated that she was once saved by the Lifeboats even if it was not in Northumbria.