Revenues from digital books rose 89% Y-o-Y in the first half of 2012

"The Publishers Association’s Sales Monitor shows that the total invoiced value of digital fiction books sales reported by participating companies saw a huge increase of 188% by value in January-June 2012 in comparison to the same period in 2011. Other strongly performing categories include children’s digital books and digital non-fiction books, which increased by 171% and 128% respectively during the same period. Overall digital sales of general consumer titles (including fiction, non-fiction and children’s) increased from £30m to £84m between January-June 2011 and 2012.
These increases reflect overall growth of 89.1% in digital sales (from £77m to £145m), while physical book sales fell 0.4% by value (from £985m to £982m) and 3.8% by volume (from 260m to 251m) over the period.
The total value of sales (digital and non-digital) increased by 6.1% in January-June 2012 in comparison to the same period in 2011, leading to £1.1bn revenue in the first six months of the year.  Digital sales accounted for 12.9% of the total value of sales in January-June 2012, up from 7.2% in the equivalent period in 2011"

Source:  Press release from the Publishers Association, 18th September 2012