Zilch is currently offering £15 when you sign up for their buy now, pay later service.
Simply sign up using a referral link and proceed to verify yourself (email and ID). After this you'll have £15 worth of reward points which you can spend anywhere Mastercard is accepted. Just click Zilch anywhere. Make sure you select the option to pay the full amount and also slide the slider which lets you use your reward balance.
This is a great offer as you can spend your reward instantly.