Random House (UK) also confirmed this week that EL James's erotic novel had sold over four million physical and ebooks combined in the UK, Australia, New Zealand, India and South Africa.
Physical paperback sales measured by Nielson Bookscan put the UK sales of the book at 765,000 copies. Arrow Books has reprinted the novel 16 times in the UK.
"The sales figures are phenomenal and we look forward to seeing them grow over the summer - what could be more perfect than relaxing by the pool with a copy of Fifty Shades of Grey," said Arrow's director of publicity and media relations Charlotte Bush.
"I speak from first hand when I say the books are utterly addictive and I know I'm not alone - everyone here at Arrow Books is totally Grey-sessed!"
Charts editor of The Bookseller Philip Stone added: "Sales of the Fifty Shades series have been nothing short of phenomenal and records are tumbling.
"All three novels sold more than 100,000 copies at UK bookshops last week, meaning EL James has become the first writer to see three of her books sell more than 100,000 copies in the same week."
He added: "The paperback edition of Fifty Shades of Grey has sold in just two months (765,000+ copies) what Brown's The Da Vinci Code, the bestselling paperback novel of all time, took over six months to achieve.
"An article yesterday said that Fifty Shades of Grey 'may reach the million mark' in paperback sales by the end of the year. The end of the year? I think it'll hit that figure by the end of the month."
Arrow also confirmed that EL James will make her first public appearance in the UK at a London event on July 3.