Previously unpublished Harry Potter material will be released on a new website in a move described by author J.K. Rowling as a “give-back” to her millions of fans.

Details about some of the famous characters in the series and an in-depth explanation of Quidditch – the fictional sport played by the student wizards in the best-selling books – are promised.

Speaking at a press conference at the Victoria and Albert Museum in Kensington, central London, Ms Rowling said the Pottermore site was a place for fans to “share” the books.

She said: “I wanted to give something back to the fans that have followed Harry so devotedly over the years, and to bring the stories to a new digital generation.

“I hope fans and those new to Harry will have as much fun helping to shape Pottermore as I have.

“Just as I have contributed to the website, everyone else will be able to join in by submitting their own comments, drawings and other content in a safe and friendly environment – Pottermore has been designed as a place to share the stories with your friends as you journey through the site.”

Fans will be able to work their way through the books and follow Harry to Hogwarts.

They will be sorted into one of the school’s rival houses and become student wizards themselves by casting spells and mixing potions.

The interactive website, which includes elements of social networking and computer games, allows fans to access material cut from the original books and read new insights from the author along the way.

Ms Rowling said the idea partly came because of the demand for eBooks of the novels.

She said: “I wanted to pull it back to reading, I wanted to pull it back to the literary experience, the story experience and this is what emerged.”

She said some of the material for the website had been “literally” dug out of boxes.

Some has been written specially for the website but “almost half” of it was already written or in note form.

She added fans might still see the publication of a Harry Potter encyclopaedia, with all profits going to charity, but she would not publish another novel about the character.

Potter fans can register for an online challenge that goes live on the website on July 31.

One million will be chosen to join Pottermore early and help the site develop.

The website, which includes an online store where fans can buy eBooks and digital audio books, will be open to all in October.

Ms Rowling admitted that working on the project, which has been in development for several years, had allowed her to “stay in touch” when she was writing the stories.

The site, which will be free to join, will eventually include links and material from all the Harry Potter novels.