From The Publishers Association:
Digital sales accounted for 12 per cent of UK publishers’ total revenues of £3.3bn [approx. $5.14 billion/USD] in 2012 , according to the Publishers Association (PA) Statistics Yearbook.
Publishers’ total sales revenues – physical and digital – rose 4%. Total digital sales rose 66 per cent, to £411m, and total fiction digital sales rose 149 per cent, to £172m.
The PA Yearbook 2012 also recorded an increase of 4 per cent in home physical sales of children’s books (£233m), and an increase of 6 per cent in home physical sales of school books (£172m). Total physical sales of fiction books were also up, by 3 per cent, to £502m. Physical and digital sales of fiction books were up by 21 per cent to £674m, and digital sales of non-fiction/reference books were up 95 per cent, to £42m.