People wait in a line to buy E.L James's new book 'Grey: Fifty Shades of Grey as Told by Christian' outside the Barnes and Noble store on Fifth Avenue in New York on June 18, 2015. PHOTO: JEWEL SAMAD
People wait in a line to buy E.L James's new book 'Grey: Fifty Shades of Grey as Told by Christian' outside the Barnes and Noble store on Fifth Avenue in New York on June 18, 2015. PHOTO: JEWEL SAMAD
Author EL James poses for photographers before signing her new book 'Grey' at a Barnes & Noble bookstore in New York on June 18, 2015.  Photo: Mary Altaffer
Author EL James poses for photographers before signing her new book 'Grey' at a Barnes & Noble bookstore in New York on June 18, 2015. Photo: Mary Altaffer

It's been described as "about as sexy as a misery memoir". But the critical derision which greeted EL James's new Fifty Shades of Grey spin-off did not prevent the novel setting sales records as millions of fans snapped it up.

Published last Thursday, Grey retells the story of the S&M relationship between Christian Grey and shy student Anastasia Steele, from the perspective of the controlling businessman.

Its British author said her fans had "asked … and asked … and asked … and asked" for the alternative version.

She has been proved right. The publisher Vintage, which released the book in the US on 18 June, said it had sold 1.1 million copies to date across paperback, ebook and audiobook in North America alone. In the UK, publisher Arrow Books said the novel had smashed the record for the biggest first-week sales for an adult title. Grey sold 647 401 copies in physical and ebook combined in its opening three days of sale in the UK.

The previous largest first-week sale in Britain was for Dan Brown's The Lost Symbol which sold just under 551 000 copies in the five days following its publication in 2009.

Susan Sandon, managing director of Cornerstone, part of the Random House group which owns Arrow, said: "The excitement and enthusiasm that Grey's publication has generated is totally irresistible and I am delighted with these early results."

Amazon sales of Grey have been boosted by a heavily discounted sale price of just £3.85 for the paperback. The title is part of a "three paperbacks for £10" Amazon promotion. The Kindle edition, certain to find its way on to thousands of readers ahead of the summer holidays, is selling for £3.66.

Grey is certainly outperforming James's original Fifty Shades of Grey, which sold 14 814 copies in its first week, although it went on to become the best-selling debut of all time.