Auctioneers in Wotton-under-Edge have unearthed a rare children's book during a routine valuation visit – and the unusual find is now estimated to deliver a value of several thousand pounds when it goes under the hammer next week.

Where the Wild Things Are was written by American author and illustrator Maurice Sendak. First published in 1963, it has become a firm favourite with youngsters around the world and has sold more than 19m copies – despite the fact that a social backlash on its release saw it being banned in parts of the USA because critics thought the imagery was too frightening for children. 

By 2009 though, the inspirational novel had been made into a big-screen live action film.

English composer Oliver Knussen also composed a fantasy opera of the same name, scoring the music between 1979 and 1983 on commission from the Opera National, Brussels.

The work premiered at the Theatre de la Monnaie in November 1980, and the final version was first performed by the Glyndebourne Touring Opera at the National Theatre in London in January 1984.

Joseph Trinder, Auctioneer and Valuer said: "This is a quite unique find. It has been signed by the author, Maurice Sendak, who has also hand drawn one of the monsters from the story and carries the inscription, 'for Jean', dated October 1984.

Further key details relate the book to the subsequent musical, he added: "The book also has an illustrated musical stave with a note, 'for Jean, with warmest wishes, Oliver Knussen'."

The work came to light, he said, during a routine valuation visit in Wiltshire and the auction house at Wotton-under-Edge's Tabernacle Pitch has now placed an estimate of £3,000-£5,000 in the lot when it comes up for auction at its Autumn Quarterly Fine and Curated Sale (Tuesday, September 16).

● The plot focuses on a young boy, Max, who wreaks havoc in his household and is sent to bed without any supper. His bedroom transforms into a jungle and he travels to an island inhabited by monsters known as the Wild Things. The book won the annual Caldecott Medal from children's librarians in 1964, citing it as the previous year's "most distinguished American picture book for children".