A “rare, unique and incredibly exciting” collection of original letters and drawings sent between the creators of Winnie-the-Pooh are set to go under the hammer this week, after being discovered in a carrier bag.

The collection includes a series of written exchanges between AA Milne, the author behind the iconic children’s literature character, illustrator EH Shepard and their publisher, Frederick Muller.

The collection belonged to the late Leslie Smith, who founded the publishing company Cressrelles. His company had taken over another publishing company that had been run by the family of Winnie-the-Pooh publisher Frederick Muller, leaving Muller’s letters in Smith’s possession. The letters – some of which had not been seen by anyone since 1926 – were found by Smith’s children while clearing out their father’s loft after his death in November 2023.

Will Farmer, director at Fieldings Auctioneers which is arranging the sale, received the material “about five months ago” when the family were unsure of what to do with it.

Aided by BBC Antiques Roadshow’s Clive Farahar, they combed through the findings, having previously assumed that all documents from the era had been accounted for.

The unearthed archive contains first-draft manuscripts of works by Milne such as his poem Wind on the Hill and an opening dedication for the 1927 poetry collection Now We Are Six, in addition to a drawing of Winnie-the-Pooh and Piglet in the snow.

There is also a stern reprimand written by Milne on behalf of the anthropomorphic bear, in response to an Observer crossword that referred to the character as a “fabulous monster”. Milne noted to Muller that “Pooh strongly objects”, adding that the bear was threatening to come to the publishing house and make his position clear.

Traces of “creative tension” between Milne and Shepard, and mediated by Muller, are evident in the letters, with the former stating that “[Shepard] must do new drawings for April and September as the originals are very poor.”

Milne also displayed moments of impatience with his co-creator’s tardiness. In one letter to Muller he wrote: “If Shepard has not done the new drawing yet, then he need not.”

For his part, Shepard appeared to be contending with housing issues at the time and defended the delay to Milne, explaining that “I am doing my best to hurry on the drawings, but style is rather cramped by the blasted move, [which] as you will see from the above address, has been accomplished.”

“Thursday, Friday, Saturday, were, to put it mildly, bloody …”

According to Fieldings, the estimated value of various documents range from £100 to £1,500. But they could sell for even more: similar items have found buyers willing to make record-breaking purchases. For example, in 2018, an original Winnie-the-Pooh map by Shepard sold for £430,000.

Farmer noted that news of the find has generated worldwide interest from potential buyers, particularly in the UK and the US.

While the bulk of the material relates to the honey-loving bear and his assortment of friends, the letter collection also contains correspondences from other writers, including Enid Blyton and JRR Tolkien.

In one correspondence with Muller, Blyton discusses advertising space and expresses preference for her next book to be publicised on back covers.

Elsewhere, Tolkien addresses handwritten postcards to Smith about the minutiae of typefaces and making arrangements to collect an awards trophy. Smith’s son, Simon, who now runs Cressrelles, remembers his father describing the Lord of the Rings author as someone with “incredible wit and humour, but the most atrocious man at meeting deadlines.”

Simon Smith is hoping that the sale of these letters will raise enough money to invest in an institution studying the work of Milne. The auction is expected to take place this Thursday, ahead of National Winnie-the-Pooh Day on 18 January.

Described as “the most famous bear in literary history”, stories featuring Winnie-the-Pooh have been translated into multiple languages including Faroese, Latin and Yiddish.

Inspiration for the character was sparked by a teddy bear belonging to Milne’s son, Christopher Robin, and the archive collection includes a birthday book of drawings from Milne and Shepard dedicated to him.