Walter Mitty and Billy Liar

Is Keith Waterhouse's Billy Liar (1959, filmed 1963) derived from James Thurber's Walter Mitty (1939, filmed 1947)? I did not find an answer.

Interestingly the similarity of the characters is noted here in a December, 1963 (not 1961, as shown on the web page) movie review.

Ah Q, a creation of Lu Xun in 1921, bears a more remote resemblance to these characters.

ps. A recent Guardian aritcle on the cultural impact of Billy Liar, the movie.