The option to download purchases and synchronise Nook libraries will disappear on May 31st. At that point, customers will be asked to use the Sainsbury's app, where the "vast majority" of Nook books are available to download and read. Existing purchases, if they're in stock, will be instantly redeemable -- customers won't need to purchase them again -- and vouchers will be available for titles that aren't transferable. Sainsbury's has an Android app for ebooks, so customers with a Nook tablet should be fine. What isn't clear, however, is how Nook e-readers will be supported.

Barnes and Noble hasn't said why it's leaving the UK ebook market. However, we think we can sum it up in a single word -- Amazon. The online retailer is the dominant brand for ebooks, with a refined suite of Kindle e-readers and a ruthlessly priced Kindle Store. It's difficult for anyone to compete now, even juggernaut companies like Sony and Tesco. Apart from Kobo, which is backed by Rakuten, how many Kindle competitors are left? We're struggling to come up with many names.