American actor Gene Wilder as Willy Wonka in 'Willy Wonka & The Chocolate Factory', directed by Mel Stuart, 1971. (Photo by Silver Screen Collection/Hulton Archive/Getty Images)

The book grew out of a bedtime story Dahl made up for his first two children, Olivia and Tessa (the second of whom would go on to become the mother of the writer, presenter and model Sophie Dahl).

The original title of the book was Charlie's Chocolate Boy. Charlie was one of ten children who found one of what was then a weekly batch of golden tickets entitling them to a tour of the factory and ended up in a chocolate boy mold by accident and being bought for a little girl as an Easter present.

Mr. Willy Wonka was first known as Mr. Ritchie.

And the Oompa-Loompas, right up until the very last moment, were the Whipple-Scrumpets.

The 1971 film adaptation of the book came about because Mel Stuart's daughter Madeline brought a copy home, told him she had read it three times and that she wanted him to make it into a film. Coincidentally, his producer partner David Wolper was having a conversation with an advertising agent who had a client -- Quaker Oats -- who wanted to fund a project that could tie in with a new chocolate bar they were making. Done and done!

Dahl wanted Peter Sellers or Spike Milligan to play Wonka in the film. Stuart and Wolper wanted all-singing, all-dancing, all-Tony-Award-winning stage actor Joel Grey, but realised that if any of the child actors had a growth spurt during shooting they could end up towering over the five-foot-five star. And then, when Gene Wilder auditioned they knew they had found the perfect man for the part. "The role fit him tighter than Jacques Cousteau's wetsuit," says Wolper in his autobiography, Producer.

Julie Dawn Cole, who played Veruca Salt in the film, is now a child psychotherapist. Peter Ostrum -- Charlie -- is a big animal vet in New York State.

There are five drafts of Charlie still in existence, in the archive at the Roald Dahl Museum and Story Centre in Great Missenden, Buckinghamshire. It is thought that Dahl destroyed the very first one after his young nephew told him it was "rubbish."

When it was first published in September 1964 it sold 10,000 copies in the first week. The New York Times called it "sheer joy."

Dahl wanted a relatively unknown young artist called Maurice Sendak to illustrate the first edition. But he was too busy working on a book that the timing suggests was Where the Wild Things Are.

Lucy Mangan is the author of Inside Charlie's Chocolate Factory (Puffin, September 9). For more about the 50th anniversary of Charlie and the Chocolate Factory, go to www.roalddahl.com.

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