Jenny Colgan said it was “a bit like peering into the inside of your dog’s head”; Bryony Gordon found it “about as sexy as a misery memoir and as arousing as the diary of a sex offender”. But no matter: the fans of EL James have chosen to decide for themselves – and have bought more than 1m copies of Grey, the latest in her Fifty Shades series, in the US, and 647,401 in the UK.

Released last Thursday, Grey tells the story of the S&M-focused relationship between businessman Christian Grey and shy student Anastasia Steele from the perspective of Christian – something its British author James writes in her dedication that fans had “asked … and asked … and asked … and asked” for.

Early sales indications from America show she was right: according to Vintage, which released the book in the US on 18 June, it has sold 1.1m copies to date across all editions – paperback, ebook and audiobook. Vintage publisher Anne Messitte told US trade magazine Publishers Weekly that the figure “speaks to the engagement and passion readers have for the Fifty Shades books”, adding: “Christian’s side of the story is proving to be irresistible.”

In the UK, Grey sold 385,972 print copies in the three days until 20 June, according to book sales monitor Nielsen BookScan, and 261,429 ebooks, according to publisher Arrow, giving a total sale of 647,401. This makes it the fastest selling adult title ever in the UK - the record for a first-week sale for an adult title was previously held by Dan Brown’s The Lost Symbol, which was published in October 2009 and sold 551,000 print copies in its first five days on sale.

“We’ve had magnificent support from across the trade,” said Susan Sandon, managing director of Cornerstone. “The excitement and enthusiasm that Grey’s publication has generated is totally irresistible and I am delighted with these early results.”

James’s previous novels, Fifty Shades of Grey, Fifty Shades Darker and Fifty Shades Freed – which tell the story of Christian and Ana’s relationship from her perspective – have sold more than 125m copies around the world to date.