They are the two great fantasists of 20th-century literature – one a northern clerk at an undertakers who, among other daydreams, pretends to be the leader of the imaginary state of Ambrosia; the other, a hen-pecked suburban husband who uses similar flights of fancy (he steers the "eight-engined Navy hydroplane - through the worst storm in 20 years") to transform the dullness of an ordinary day shopping with his wife.

This week it was announced that Keith Waterhouse's original manuscript for Billy Liar is among the writer's papers that have been donated by his family to the British Library for the exhibition Writing Britain: Wastelands To Wonderlands, which opens in May. But here's a question: how influenced was Waterhouse by Walter Mitty, James Thurber's earlier creation?

The Secret Life Of Walter Mitty was first published in The New Yorker in 1939 and may arguably be the most famous short story ever written. It was reprinted in Reader's Digest in 1943, which is conceivably where the bright, 14-year-old Waterhouse may have read it in the library in Leeds. He would surely have seen the film, made in 1947 and starring Danny Kaye – it was a major release at the time. Such was the story's success, the term Walter Mitty, to describe anyone who fantasises about a life more glamorous or exciting than their own, entered the language and is still found in dictionaries today.

Billy Liar was published in 1959 and famously filmed in 1963. Waterhouse surely viewed his best-loved character as a tribute to Thurber and would lament the fact that the latter, who died in 1961, is virtually a forgotten writer today. Despite its occasional mention in the media, how many people below the age of 30 have heard of Walter Mitty or know his origins? However, that could change next year when a new film loosely based on the original story and starring Ben Stiller is to be released.

Though it seems the writers never met, they have another link aside from their two most famous creations. They were both invited to carve their initials in the table owned by Punch magazine. This autograph-book-on-legs is currently kept in the British Library's storage facility in Islington. One wonders if their two fictional characters stalk these quiet rooms after hours, one booming: "A man could lose himself in London!", the other crying: "We're going through -!"