Hi weejack20, welcome to Cruise-Chat! Congratulations on your upcoming cruise! Be warned, cruising is addictive
I would think, since you're boarding in England, you would pay in Euros. Just to make sure, give your local RCI agent a call or your travel agent. They will know for sure. I would imagine RCI will be able to convert and take anything, but just to make sure, give them a buzz.
Hope you have a marvelous cruise! Please come back and let us know how you enjoyed it. Best wishes!