Instructions:10% cashback too through Topcashback, probably Quidco as well but not checked.
Got this code in an email. Saved me £9-odds on a £60 order.
Best price I can find anywhere (and competitive even before the 15% discount) on the genuine Canon ink cartridges for my MP640 (CLI-521, BCI-520). Don't know about others but after the 15% discount and the 10% cashback (assuming it tracks, mine always do) then seems to be a pretty good deal. Loads cheaper than fleabay!