Roald Dahl may be best known for writing children’s stories, but when it came to adults he didn’t mince his words.

When aspiring writer Jay Williams sent the author a letter in 1980 asking for feedback on a short story he had written for an A-Level project, he never expected to get a response – let alone such a blunt one.

To his surprise, Dahl took the time to write a write to him, warning the 17-year-old to stop using so many “beastly adjectives”, and advising him to study “American short story writers”.

A letter dated 1980 that Roald Dahl sent to A-level student Jay Williams (Jay Williams)

In the signed letter, the author wrote: “I have read your story. I don’t think it’s bad, but you must stop using too many adjectives. Study Hemingway, particularly his early work and learn how to write short sentences and how to eschew all those beastly adjectives.

“Surely it is better to say ‘She was a tall girl with a bosom’ than ‘She was a tall girl with a shapely, prominent bosom’, or some such rubbish. The first one says it all. Yours sincerely, Roald Dahl.”

Williams, who has worked in journalism for 30 years, was taken aback when he first received the letter but says the advice has stood him in good stead.

“With the callowness and arrogance of youth, I was expecting him to say ‘wow this is amazing’…but it obviously sank in because that thing of keeping it tight really rang true as a young journalist and it has been a worthwhile lesson that I obviously learnt early on,” he said.

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Williams, who now works for PR company 72Point, rediscovered the letter recently in a box of old correspondence from his Mum, and posted a picture of it on Twitter.

The letter received an overwhelming response, gaining over 1,000 retweets and favourites in a few days thanks to a retweet from the Roald Dahl Literary Estate's Twitter account.

Rachel White, collections manager and archivist at the Roald Dahl Museum & Story Centre, said the letter is written in Dahl’s “trademark acerbic tone”.

“It’s a very typical letter from him – he was to the point and could be very sharp," she said.

"He did receive a lot of letters from people asking for advice, and as he got older his replies were slightly more crabby. It contrasts quite a lot to his letters to children, which were lovely and kind. They would start ‘hello gorgeous Ida and all the children in her class’.”

The letter will be included in a forthcoming book about Dahl’s letters, to be published next year.