Sir Terry Pratchett's Discworld novel The Wee Free Men is to be adapted for the big screen by Muppets creators The Jim Henson Company.

First published in 2003, The Wee Free Men was Pratchett's 30th novel to be set on Discworld, a fantasy realm consisting of a flat planet, resting on the back of four elephants, standing on the shell of Great A'Tuin, a giant space turtle of unknown gender.

The comedic novel was one of the first to be published as part of the 'YA' Discworld strand, a collection aimed at children and young adults. It focuses around heroine Tiffany Aching, a nine-year-old trainee witch. In the story, the young witch-to-be must defend her home against the monsters of Fairyland. Luckily she has some very unusual help: the local Nac Mac Feegles - aka the Wee Free Men - a clan of fierce, sheep-stealing, sword-wielding, six-inch-high blue men who speak a form of language which is what we would consider to be a cross between Glaswegian and Scots Gaelic. Together they must face "headless horsemen, ferocious grimhounds, terrifying dreams come true, and ultimately the most powerful force of all - the Queen."

The film will be produced by Brian Henson, son of the late Jim Henson, with The Jim Henson Company set to work with Narrativia, a company co-directed by Rhianna Pratchett, daughter of the later author. She has had a long-time ambition to adapt her father's book for the cinema, and has written the screenplay. She says: "I've loved The Jim Henson Company's work all my life, so it's a great honour to team up with them and bring Wee Free Men to the big screen."

Brian Henson adds: "As a family owned company, we fully understand the importance of legacy properties. The Discworld series is a richly developed world with devoted fans, myself included, and there is no-one better than Rhianna to bring Terry's beloved project to life on the big screen."

Pratchett, who died last year, wrote 41 Discworld novels, which have together sold over 80 million copies. The Wee Free Men will be the first Discworld book to become a film, however a number of the novels have previously been adapted for television and radio. The most recent adaptation was in 2013, Radio 4's Eric, whilst the last on-screen adaptation was Sky1's Going Postal in 2010.

Further details on the project to adapt The Wee Free Men is expected at a later date. No casting or planned release date has yet been revealed.