Sales data for 2009 suggests that one in five books sold in the UK are now bought from three supermarkets: Tesco, Asda and Sainsbury’s. The volume share for Tesco is around 10 per cent.
You can read the original Bookseller report here
In Inside Book Publishing in u.s we write about the growth in supermarket sales:
apr 28, 2014 – Both Borders and Waterstone’s would be sitting pretty in the retail market
were it not for the growth in sales through the internet and supermarkets. …
The supermarkets have become so significant to consumer publishers that
in 2007 HarperCollins launched a new mass market list called Avon, aimed
at time-pressed women. Called ‘channel publishing’, the list was to take ‘a
supermarket-style approach, identifying the three most popular genres for [the]
audience: chick lit, romance, and crime/thrillers’ (The Guardian, 31 March 2007).
Supermarkets can call the shots, as they do in other product areas, demanding
large discounts as well as payments to remain preferred suppliers. Publishers
have to respond not only by changing what they publish but also by forming larger
groups, which can offer a constant supply of likely bestsellers.