Once you've selected your chosen items, proceed to the checkout, enter your delivery details and progress to the Payments page.
Select Pay with Gift Card and enter the 16-digit code found on the reverse of the Gift Card exactly as shown, with no spaces or additional characters. Click Apply, and the value of the Gift Card should be deducted from the total shown.
For more information or for the full Gift Card T&Cs, please follow the link here.