Jk Rowling's new book 'The Casual Vacancy' has failed to impress critics.

The 'Harry Potter' author's first adult novel shot to the top of best-seller lists after selling 2.6m copies on pre-order, but the gritty tale has so far received mixed reviews from literary critics.

The New York Daily News paper has slammed the book, saying: ''J .K. Rowling has gone from Potter to potty-mouth. It isn't dreadful. It's just dull ... We've read it before, darker, bleaker and better.''

The Telegraph newspaper is also less than complimentary, explaining: ''It quickly becomes clear that this is not the book we might have been expecting.''

'The Casual Vacancy' is a great departure from JK's beloved children's fiction about the wizarding world, and the racy tale set in the fictional town of Pagford features self-harm, drugs, heavy swearing, sex and even a rape scene.

However, The Guardian found redeeming qualities in JK's novel, describing it as ''no masterpiece, but it's not bad at all: intelligent, workmanlike, and often funny.''

The reviewer added: ''I could imagine it doing well without any association to the Rowling brand.''

Despite this lukewarm response, the book is one of the most hotly-anticipated novels of the year and is predicted to do well.

'The Casual Vacancy' is released today (27.09.12).