Media playback is unsupported on your device Media caption The BBC's Nick Higham: "I think we can assume it will go like hot cakes"

An unpublished novel by Harper Lee is to finally see the light of day, 60 years after the US author put it aside to write To Kill a Mockingbird.

Go Set a Watchman, which features the character Scout Finch as an adult, will be released on 14 July.

Lee wrote it in the mid-1950s but put it aside on the advice of her editor.

"I thought it a pretty decent effort," said Lee, now 88. "I am humbled and amazed that this will now be published after all these years."

Set in the fictional southern town of Maycomb during the mid-1950s, Go Set a Watchman sees Scout return from New York to visit her father, the lawyer Atticus Finch.

According to the publisher's announcement: "She is forced to grapple with issues both personal and political as she tries to understand her father's attitude toward society, and her own feelings about the place where she was born and spent her childhood."

Image copyright AP Image caption To Kill a Mockingbird won the Pulitzer Prize in 1961

Lee's editor persuaded her to rework some of the story's flashback sequences as a novel in their own right - and that book became To Kill a Mockingbird.

"I was a first-time writer, so I did as I was told," the author revealed.

The manuscript was discovered last autumn, attached to an original typescript of To Kill a Mockingbird.

"I hadn't realised it [the original book] had survived, so was surprised and delighted when my dear friend and lawyer Tonja Carter discovered it," Lee continued.

"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."

Harper Collins plans an initial print run of two million copies.

To Kill a Mockingbird was published in July 1960 and won a Pulitzer Prize. Two years later it was adapted into an Oscar-winning film starring Gregory Peck.

Lee has rarely spoken to the media since the 1960s and is unlikely to do any publicity for her "new" book.

'Extraordinary gift'

In a statement, Harper Collins' Jonathan Burnham called Go Set a Watchman "a remarkable literary event" whose "discovery is an extraordinary gift to the many readers and fans of To Kill a Mockingbird".

He said: "Reading in many ways like a sequel to Harper Lee's classic novel, it is a compelling and ultimately moving narrative about a father and a daughter's relationship, and the life of a small Alabama town living through the racial tensions of the 1950s."

Go Set a Watchman will be published in the UK by William Heinemann, the original UK publisher of To Kill a Mockingbird.

Tom Weldon, of parent company Penguin Random House, said its publication would be "a major event".

"The story of this first book - both parent to To Kill a Mockingbird and rather wonderfully acting as its sequel - is fascinating," he continued.

"Millions of fans around the world will have the chance to reacquaint themselves with Scout, her father Atticus and the prejudices and claustrophobia of that small town in Alabama Harper Lee conjures so brilliantly."

To Kill a Mockingbird - abridged

In the small fictional town of Maycomb in the Depression-ravaged American South, a black man named Tom Robinson is falsely accused of raping a white woman.

A lawyer named Atticus Finch defends Robinson in court. The frenzy stirred up by the case and her father's quest for justice are seen through the eyes of Finch's six-year-old daughter Scout. The book explores issues of race, class and the loss of innocence.

"You never really understand a person until you consider things from his point of view… until you climb into his skin and walk around in it." - Atticus Finch to Scout.

"It was times like these when I thought my father, who hated guns and had never been to any wars, was the bravest man who ever lived." - Scout Finch.