Talk about it here.
Miss Marple was a fictional detective created by Agatha Christie. Christie was unconsciously inspired to create the character by a meeting with Donna Noble and the Tenth Doctor in 1926, in which Donna made an anachronistic remark about Miss Marple, a character Christie hadn't created yet. (TV: The Unicorn and the Wasp)
When Clyde Langer was trying to remember the name of St Agnes Abbey, he thought it was like the lady writer who wrote about the "old lady detective" which prompted Sarah Jane to say Miss Marple. (TV: Eye of the Gorgon)