Harper Lee's second novel, Go Set a Watchman, topped the US bestseller list in 2015, selling 1.6 million copies more than half a century after her Pulitzer-winning first book To Kill a Mockingbird was published.

The figures were based on US print unit sales reported to Nielsen since the novel was published in July, snapped up by avid fans who for decades thought the reclusive author would never publish another word.

Pre-orders turned it into an instant bestseller at many retailers the moment its release was announced by publishers HarperCollins last February.