I can't see them getting their knickers in a twist about this - after all, they're now in a position to do what they want, any old time.
However, given they supply the Radio1 chart, have a look
here.
They list the following "official" download sites:
iTunes, Napster, MyCokeMusic, Woolworths, 7 Digital Media, Playlouder, MSN Music, Big Noise Music, HMV, Virgin, Tesco, Tiscali Music, Sonic Selector, Wanadoo, city16.com, recordstore.co.uk, KarmaDownload, Wippit, The Music Engine Service, Bleep, easyMusic
...but whether this is definitive and all-inclusive, I don't know.