To Kill A Mockingbird fans may feel "baffled and distressed" at Harper Lee's much-anticipated follow-up due to its hero lawyer Atticus Finch "shockingly" portrayed as a racist "bigot" who went to a Ku Klux Klan meeting, according to a review.

The new novel, Go Set A Watchman, is out on Tuesday and is already a guaranteed best-seller as the follow-up to Lee's 1960 book about a rape trial in the racially-divided deep south of the US.

Mockingbird and its central characters, Scout, her brother Jem and their lawyer father Atticus, were brought to life in a 1962 film starring Gregory Peck.

Go Set A Watchman revolves around the now-adult Scout's return to her native Alabama from New York to visit her father.

But according to a review in the New York Times, fans of Mockingbird will be introduced to a different side of Atticus.

The review says: "We remember Atticus Finch in Harper Lee's 1960 classic, To Kill a Mockingbird, as that novel's moral conscience: kind, wise, honourable, an avatar of integrity who used his gifts as a lawyer to defend a black man falsely accused of raping a white woman in a small Alabama town filled with prejudice and hatred in the 1930s."

It adds: "Shockingly, in Ms. Lee's long-awaited novel, Go Set a Watchman (due out Tuesday), Atticus is a racist who once attended a Klan meeting, who says things like 'The Negroes down here are still in their childhood as a people.' Or asks his daughter: 'Do you want Negroes by the carload in our schools and churches and theatres? Do you want them in our world?'"

The review later adds: "The depiction of Atticus in Watchman makes for disturbing reading, and for Mockingbird fans, it's especially disorienting. Scout is shocked to find, during her trip home, that her beloved father, who taught her everything she knows about fairness and compassion, has been affiliating with raving anti-integration, anti-black crazies, and the reader shares her horror and confusion.

"How could the saintly Atticus - described early in the book in much the same terms as he is in Mockingbird - suddenly emerge as a bigot? Suggestions about changing times and the polarising effects of the civil rights movement seem insufficient when it comes to explaining such a radical change, and the reader, like Scout, cannot help feeling baffled and distressed."

News of the new book's publication stunned the literary world earlier this year and concerns were raised about the extent of Lee's involvement in the project.

Her agent was forced to respond to reports suggesting the 88-year-old was being taken advantage of over the publication of the book.

Authorities in her native Alabama closed their investigation into the issue saying the reclusive writer had ''made it quite clear'' she wanted the book published.

Lee has previously said: ''In the mid-1950s I completed a novel called Go Set a Watchman.

''It features the character known as Scout as an adult woman and I thought it a pretty decent effort.

''My editor, who was taken by the flashbacks to Scout's childhood, persuaded me to write a novel from the point of view of the young Scout.

''I was a first-time writer, so I did as I was told. I hadn't realised it had survived, so was surprised and delighted when my dear friend and lawyer Tonja Carter discovered it.

''After much thought and hesitation I shared it with a handful of people I trust and was pleased to hear that they considered it worthy of publication.

''I am humbled and amazed that this will now be published after all these years.''

Waterstones shops in Glasgow, Manchester, Leeds, Liverpool and Nottingham will open so fans can buy a copy at one minute past midnight on Tuesday.