A letter “written” by Winnie the Pooh is expected to fetch up to £6,000 at auction.

The note was penned on embossed letterhead paper 85 years ago by Pooh illustrator E H Shepard in reply to a birthday party invitation from an 11-year-old boy to the fictional bear.

It is littered with misspellings, to make it authentic, and a drawing of a crying Pooh with his friend Piglet and was sent to the son of birth control pioneer Marie Stopes, who was a close friend of the illustrator.

The note is addressed to “Buffkins”, as Dr Stopes’s son, Dr Harry Stopes-Roe, was known as a child.

It reads: “We are teribly sorry that we shant be able to come to your party on March 30th but we are going to be away. Thank you so very much for inviteing us.”

The letter is being sold by the Stopes-Roe family and will go on sale at Dominic Winter Auctioneers in Cirencester, Gloucestershire, on June 24.

Auctioneer Chris Albury said: “It’s such a charming Winnie the Pooh collectable that will be coveted by thousands of Pooh and Piglet fans of all ages worldwide.

“The Marie Stopes family connection is interesting too and the friendship between Shepard and the birth control pioneer and her son will be news to many.”

Also going under the hammer from the same collection are two pencil drawings, signed and dated July 1929, showing the five-year-old Christopher Robin-lookalike Stopes-Roe climbing a tree and riding a pony.

Each drawing is estimated to fetch between £1,500 and £2,000.

Stopes-Roe was a well-known humanist and was married to the daughter of illustrious scientist, engineer and inventor Sir Barnes Neville Wallis. He died in 2014.

Shepard, who died in 1976, was an illustrator for Punch magazine for 50 years, though he remains best known for his Pooh illustrations.