Smaller bags are buy one get one free, larger 12 kilo bags are buy one get one half price. The larger bags are already discounted by £10 - the offer for larg bags isn't working on the site, but if you order the food & ring them, they will credit you back the difference.
The10% off code R7THJ9XS works as well, even on old accounts, so a real bargain! I've just paid £107.96 for 4 sacks of dog food (119.96 before 10% discount) and then called them to get £29.99 credited back, so just over 20 quid a sack delivered, instead of usual price about £40!
Go quick though - the offer is only on until 2pm Tuesday and stocks normally go really quickly!