You've got plenty of time to aquire a credit card before Feb. Regards.
You can as Wilba says get a credit card and then pay it of when you get the bill we have one just for holidays? you can load your account with cash (Risky) or use your card then pay it off on the last day you could use some US$ if you have any,or ask P&O will they accept a travel card that has money loaded on it such as the post office issue/.
Sorry gave you some bad info they accept Credit card also Visa/delta debit card you can settle your account by cash or travelers cheques but you must register a credit card at check in they will not accept a pre paid card?