Leslie Bricusse (1931-) is a noted musical playwright with a much spottier track record in film.
His stage career includes at least one classic, Stop The World I Want To Get Off, starring his regular partner, Anthony Newley.
As for getting into film as a screenwriter, he got his big break replacing Alan Jay Lerner (who stalled for over a year) in 1966 to write the film version of Doctor Dolittle and quickly impressed producer Arthur Jacobs with a wealth of story ideas from their first meeting and followed up with a full treatment with song suggestions in two months later. However, the realities writing for such a Troubled Production proved a nightmare, especially working with Rex Harrison who was being a Prima Donna Jerkass who demanded endless contradictory rewrites while continually insulting Bricusse and secretly looking into replacing him with Michael Flanders and Donald Swann. Furthermore, Bricusse himself blundered when he accidentally took an original plot point from a competing would-be producer's script and put it in his own story and got the studio into a $4.5 million plagiarism lawsuit. In the end, Bricusse would get an Oscar for the song "Talk to the Animals".
Bricusse later followed with musical film versions of Scrooge (1970) and Willy Wonka & the Chocolate Factory, which both performed poorly but featured such classic songs as "Thank You Very Much" in the former and "The Candyman" and "Pure Imagination" in the latter.