The Casual Vacancy, JK Rowling’s first adult book, to be published on Thursday

JK Rowling said her next novel would be for adults and it seems she has succeeded.

Days before its official launch, excerpts from JK Rowling’s first book in the post-Harry Potter era have begun to emerge online – and it is clear that it is for grown-up eyes only.

While the full text of The Casual Vacancy is a closely guarded secret, an American journalist who has read it in the offices of publishers Little, Brown has revealed some of the book’s more risqué passages.

Far from her usual wizard descriptions of fantastical battles between good and evil, JK Rowling’s new tale is said to be one of class warfare, prostitution, heroin addiction and teen sexuality.

A female character is introduced with the description that the “leathery skin of her upper cleavage radiated little cracks that no longer vanished when decompressed”.

At another point in the book, the reader meets a “lustful boy” who sits on a school bus “with an ache in his heart and in his b****”.

And the author’s usual fans may also be shocked – if not a little perplexed – by the mention of one girl’s “miraculously unguarded v*****”.

Although some fans may be upset by the direction she has taken, JK Rowling – who has sold 450 million Harry Potter books worldwide, amassing a personal fortune of £560 million ($880 million) – insists she should be free to write about whatever she wants.

“There is no part of me that feels I represented myself as your children’s babysitter or their teacher,” she said.

“I was always, I think, completely honest.

“I’m a writer, and I will write what I want to write.”

JK Rowling, who has three children, also revealed that she was ready for a change in genre after years of writing magical tales.

“I had a lot of real-world material in me, believe you me,” she told the New Yorker magazine.

“The thing about fantasy – there are certain things you just don’t do. You don’t have sex near unicorns. It’s an ironclad rule. It’s tacky.”

However, JK Rowling, 47, insisted her decision to write for adults was “not that I just wanted to write about… sex”.

“I think there is a through-line,” she added.

“Mortality, morality, [they are] the two things I obsess about.”

JK Rowling said she drew on her own upbringing near the Forest of Dean in Gloucestershire for the novel, in which the middle-class can barely hide their loathing for the inhabitants of a neighboring sink estate.

But locals in her old home village say the portrayal of snobby residents is as much “fantasy” as Harry Potter is.

Residents in Tutshill, a small community on the English side of Chepstow, where JK Rowling used to live, said the author’s childhood could have colored her memory of village life.

JK Rowling has previously said her childhood was unhappy and she couldn’t wait to leave Tutshill.

Her mum suffered from multiple sclerosis and she had a difficult relationship with her father.

Victoria Carter, 50, told the Daily Telegraph: “I think she has a bit of a chip on her shoulder because she didn’t have a very good time in her teenage years.

“Tutshill is neither snobby nor pretentious. If it were, we wouldn’t have lived here for 22 years.”

Her husband, William, 51, a business analyst, added: “She is a fantasy writer, after all. This sounds like another of her fantasies.”

The Casual Vacancy – which is due to be published on Thursday – is already a record breaker, with the novel receiving the largest number of in-store pre-order sales this year, according to Waterstones.

It is also said to have reached well over a million online pre-orders.