Instructions:When you get to the checkout, just enter 918UAC in the Promotional Code field.
There is *no* minimum spend.
As postage is £2.99 for orders less than £15, you may view this as free postage.
If you are ordering more than £15, postage is free anyway, so you may then view this as a straight discount.
I found this by playing around with the last (now expired) code until I got lucky :-)