Pride and Prejudice

The timing is the evidence. Fielding was writing the Independent column that became the novel while the BBC serial was airing and the country was talking about it, and she has said the book is a straight lift of Austen's plot on the grounds that Austen had already done the structural work. She named the hero Mark Darcy. Four years later the films cast Colin Firth, the serial's Darcy, in the part, which is the borrowing acknowledged on screen.

Andrew Davies's six-part BBC serial, with Jennifer Ehle and Colin Firth. Six hours is long enough to be nearly complete, and it is: the letters, the Gardiners, Lydia's elopement and the second proposal all survive at length. The lake is not in the novel. Davies invented Darcy diving into the water at Pemberley and meeting Elizabeth wet through, and it became the most famous thing about the adaptation and arguably about the character. A useful case of an adaptation adding something that then attaches itself permanently to the original.