Amazon.co.uk MasterCard provides a loyalty scheme that rewards buyer for almost every purchase.
What is Haram in Amazon.co.uk MasterCard?
Can this service be used in a Halal way?
I know of no reason why loyalty schemes (in general) would be haram, as they do not show any elements of riba, maisir nor gharar that would render such a transaction unlawful. They are merely a gift given by the company for the use of their product.
As such, the only issue with the use of the credit card would be the issue of interest payments, as signing up for such a card would require signing a contract to pay interest on any unpaid balance carried over each month.
This is an issue on which there is scholarly dispute; while the well-known hadith of the prophet curses not only those who collect riba but also the one who pays it, many modern scholars feel that such a contract is still halal if one is fully confident that he can pay off the balance in full every month and thus save himself from ever paying any interest charges.
Beyond that, I know no other reason why the use of such a card could be considered problematic.