Zavvi have announced they will launch a download store in December, selling music in the MP3 format, and fully integrated with their mail-order website, akin to Amazon in the US (and what HMV are also going for over here I think).
Zavvi's predecessor Virgin Megastore had an accompanying download service of course - Virgin Digital - though like HMV's original digital music offer this was a Microsoft powered system that came with its own iTunes-style player through which both a-la-carte downloads and a subscription service could be accessed. Because both stores could only be accessed via the bespoke player the service could not be integrated with the two retail chain's existing and established mail-order websites. The bespoke player concept killed both services - no one wanted to install the player, and its existence meant neither store could benefit from the obvious value of putting download options next to the buttons where customers already bought CDs.
Virgin closed down its short lived digital music venture around about the time of the Virgin Megastore buyout that created Zavvi, meaning that while the newly independent retailer took over the Megastore's online mail-order operation it wasn't saddled with its former parent company's useless download operation. Some kind of new Zavvi download offer has been expected ever since, and is now expected to launch next month.