Add the premier delivery for £4.99 to your basket on the "get deal" link to your basket then checkout as usual.
After that, when you order anything select premier delivery which is usually £4.99 per order and for the next year you will get it for free.
You are unlimited to the amount of times that you can use it and can even order more than once per day if you forget something.
As a premier customer you will also get exclusive offers and promotions.