Sue, yes you would get a full refund if you had to cancel.
There is a chance you could lose (or gain) a little money due to the echange rate on the day of your refund. Your refund amount converted back into £UK is worked out on the day of the refund not the day you paid the cruise.
I found out when I got a refund from Dollar for an overpayment, just lost a very small amount on $150.