Findings from Nielsen Book Research show that e-book share was up from one in five to one in three in the period 2012-2014, but down to 29 percent in the first quarter of 2015.
The whole UK book market (including print and digital) increased by 4 percent to 311 million in volume and £2,176m in value last year, thanks to children's and young adults titles, which were up 9 percent in sales, according to Steve Bohme, who conducts book research for Nielsen.
Print buying decreased, though, with adult fiction sales decreasing 5 percent and adult non-fiction down 4 percent.
Amazon-published and self-published titles made up 17m of those books – worth £58m – in 2014. This represents 5 percent of the overall book market and 15 percent of the digital market. The volume and value sales are similar to 2013, but up 70% since 2012.
Bohme said that consumers had an awareness of self-publishing, were positive about its impact, willing to try titles, but uncertain about genres and pricing.
The figures were presented at The Literary Consultancy and Byte the Book's Summer Digital Book Party on 5 June.