This is only for NEW customers, although obviously you can just create another account if you already have one.
Visit the link provided, add the game to your basket and proceed to the checkout...
Then at the login screen click "No, I am new to the website" and on the following page enter all your details.
It is IMPORTANT that you sign up for a credit account during the account creation, otherwise it will not work (although you shouldn't use the option of credit, just pay by card when you eventually reach the option to do so).
At the final stage when you have an opportunity to enter any promotional codes, enter ZZ082
This should give you a £25 discount, making the total including delivery 45 + 3.95 - 25 = £23.95....
If it doesn't work, you have made a mistake!!