
I e-mail them an order, or you could phone, and despite paying £35 for delivery the overall price works out much cheaper. If you go to working dog chicken for instance (
http://www.naturalinstinct.com/products/Working-Dogs-Chicken.html) underneath the add to basket it says "Buy in bulk and save". If you click on that it says about the discount. I tend to order the "working dog" varieties anyway as they are cheaper, but was told I could order any of the foods, as long as it was over 80kg, to qualify for the discount. Internet orders don't qualify, you do need to phone or e-mail.
They often have discounts, or special offers, a week or so ago the working dog turkey was £2 for 1kg. If you sign up to their newsletter you get notified of the offers.