To use the discount you have to access the UK version of the website.
Here are the instructions for how to use our UK site and use discount codes:
When you click on our site, a pop up will appear like this (if it doesn't, you have to clear your cookies and cache)
If you click at the very bottom (It's under the paypal sign) 'not shipping to (your country), click here'
That will take you to the UK version which lets you use discount codes and we can still ship internationally.