When Charles Webb, who died earlier this year, sold the movie rights to his 1963 novel The Graduate for $20,000, it earned him a place in one newspaper’s list of “the world’s biggest mugs”. (Mike Nichols’ 1967 film version grossed more than $100m.) Where does that leave Joanne Harris, who admitted this week that she let Chocolat go for £5,000? Presumably, she would be excused “mug” status by virtue of having also negotiated a £100,000 cut of the film’s box office. Even so, flogging Chocolat so cheaply surely qualifies it as the Milk Tray, rather than the Amedei Porcelana, of movie-rights deals.

The promise of wealth from film and television is the pot of gold at the end of the publishing rainbow. There is the $5m that EL James pocketed for selling the screen rights to the Fifty Shades trilogy and the $1.3m that JK Rowling got for the first four Harry Potter books alone. Dan Brown received $6m for allowing The Da Vinci Code to be adapted, while John Grisham landed a $3.75m Hollywood deal in 1993 for The Chamber when it was still at outline stage – the most ever paid at that time for anything scribbled on the back of an envelope.