The 10% is actually reward points from your previous orders. Every time you order with us we give you 10% of the total order value without postage as reward points.
Your reward points are already in the system. When you check out you will see an option to use your reward points. This is an example below. Move the slider to use as many points as you want to use. These reward points will directly reduce the amount of money you need to pay.
Each reward point is equal to 1p (One pence) so that 100 reward points is equal to £1.