Author Harper Lee had plans to write many more novels after To Kill A Mockingbird, according to a letter written before the book was published.

According to BBC News, Lee sent a letter to a friend two years before To Kill A Mockingbird appeared in 1960, in which she listed six ideas for novels that would keep her busy for the next 15 years.

In fact, the 83-year-old author has not written a full novel since To Kill A Mockingbird, which won the Pulitzer Prize in 1961 and subsequently became a runaway, global success.

Go Set A Watchman  - which she wrote before To Kill A Mockingbird -  will be published next week on July 14.

In 1958, Lee wrote to her friend Joy Brown. Brown and her husband Michael had given the young novelist financial assistance to help her leave her job to become a full-time writer.

Lee told the couple that she was trying to finish "My Novel", describing it as "the hardest damn thing to write I've ever attempted".  She also declared that she was "about six weeks' gone with another one".

Lee then went on to list ideas for future books, outlining themes and locations, with some spontaneous observations also supplied.

"Can you feed and lodge me so long?" Lee then asked.

Lee did attempt to write more after To Kill A MockingbirdThe New Yorker recently reported that, in the late 1970s, she worked on a crime novel titled The Reverend, based on a true story about an Alabama preacher who was accused of five murders.

But she later abandoned the story because she said she did not "have enough hard facts about the actual crimes for a book-length account", the magazine reported.