Rowling's new book for adults only

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-ups 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 risque passages, the Daily Mail reported.

Far from her 'fantasy' world of Potter books where good battles evil, 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", the paper reported.

Although some fans may be upset by the direction she has taken, Miss Rowling - who has sold 450 million Harry Potter books worldwide, amassing a personal fortune of 560 million pounds 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," she was quoted as telling the New Yorker magazine.

Rowling, 47, who has three children, also revealed that she was ready for a change in genre after years of writing magical tales.

"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," she added.

However, she insisted her decision to write for adults was "not that I just wanted to write about... sex".

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 over a million online pre-orders.