Despite the widespread doubts over the decision to publish Go Set A Watchman, and despite the cries of horror that went up around the world over the weekend as readers discovered that the godlike hero of To Kill a Mockingbird, Atticus Finch, had become a racist, the novel sold more than 105,000 copies in its first day on sale in the UK.

William Heinemann, the UK publisher of Go Set a Watchman, announced the figure, which covers both print and ebooks in the UK, on Wednesday morning. “It’s so fabulous to see a book dominating the news agenda and to be reminded of just how important literature and reading is to all of us,” said publisher Susan Sandon. “I speak for everyone at Penguin Random House when I say how privileged we are to be part of this piece of publishing history.”

Book sales monitor Nielsen BookScan does not generally release first-day sales figures, although in 2007 it revealed that JK Rowling’s final Harry Potter novel, Harry Potter and the Deathly Hallows, had sold 2,652,656 copies in the UK in just one day. More recently, sales in the UK of Dan Brown’s The Lost Symbol reached 551,000 print copies in its first five days on sale in the UK and EL James’s Fifty Shades of Grey sold over 664,000 in one week in 2012, according to the Bookseller. James’s sequel Grey, released last month, sold 385,972 print copies in three days and 261,429 ebooks, giving a total sale of 647,401 and breaking Brown’s record.

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Reviews of Go Set a Watchman, written by Lee in the 1950s but laid aside when her editor urged her to focus on its flashbacks to childhood, have been mixed. Michiko Kakutani’s early write-up in the New York Times called it “a lumpy tale about a young woman’s grief over her discovery of her father’s bigoted views”, highlighting the changes to Atticus. “Shockingly,” she writes, he 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 theaters? Do you want them in our world?’”

But writing in the Mail, Chocolat author Joanne Harris found Watchman a “darker, more ambivalent, more overtly political work” in which some may see “a startling reflection of the unease and racial tensions at work today in the US; a chance for us to re-examine the myth of integration”.

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“We have travelled into the past and returned to find that our present is not quite the same as we left it. Atticus Finch will never again be the white knight we once thought him,” writes Harris. “And yet the mockingbird still sings – no longer a song of innocence, but maybe one of experience; a song that combines sorrow, forgiveness – and, ultimately, a kind of hope.”

In the Guardian, Mark Lawson found Watchman “a much less likable and school-teachable book” than Mockingbird, but called reading it “a pleasure, revelation and genuine literary event, akin to the discovery of extra sections from TS Eliot’s The Waste Land or a missing act from Hamlet hinting that the prince may have killed his father”.