Promo Code is used as follows: Add new items to your cart and click Place Order. Log in to your account at mashedpotato.uk or create a new one. Next, click on [Proceed to Payment], below the items listed, you will see a box that says [Add Coupon]; tick the MASHED POTATO Coupon Code of your choice and automatically return to the checkout page, You will see that the actual payment total has been reduced.