My dog would always prefer the cat's food - but it's way too high in protein and fat (which of course makes it more appetizing for the dog!)

There are some good dry foods out there that your pup would probably eat, but you're going to have to hide the cat's dish because pups can be devious and learn that if they say 'No!' you fly to the cupboard and tempt them with goodies - at that point you've lost the battle!

Try Pets at Home brand, I've always found that to be very palatable (or at least our dog has!) - There's info on the range online