Just appeared on my Amex account. Hopefully of use to others who don't check their card offers regularly.
Buying a £20 Amazon giftcard definitely works.
Just wondering if can stack with the first time Prime Now £5 code PRIMENOW5 and get a £25 item for effectively £15 :D - Jamster128
EDIT: For Info, my card type is Amex Platinum Cashback - Jamster128