This article is from the Tom Holt FAQ, by Nick Boalch email@example.com with numerous contributions by others.
The female lead in "Flying Dutch" was called Jane (a) after a friend of
my wife's, an accountant, who's called Jane (and is nothing at all like
the character in the book) (b) because it seemed to suit her -
straightforward, quite strong, dysbimboesque, but with subliminal
associations of (i) plain Jane (ii) the dashing & adventurous heroine of
the old comic strip (iii) me Tarzan, you...
By the time I finished FD, I was using the name Jane as mental shorthand
for that kind of female character; and since it's a character type I find
useful, I stuck with the name. Female leads who don't follow that pattern
get called something else; Michelle in "Open Sesame" was a bit too mimsy
to be a Jane, Bianca in "Paint Your Dragon" needed to be rather more
glamorous, & so on. I called the female #2 lead in "Wish You Were Here"
Janice, because she's almost a Jane - by learning and suffering she
moves towards acquiring Janity.
The other reason is because it annoys the hell out of my mother.