Ooooh another thought on Credit Cards, if you do dedcide to take that option be advised the Cunard will add a 3% handling fee for exchanging the rate from $UD to £GB so you find a card which does not charge for exchanging the rate (we use the Post Office as their card has no annual fee either).
You should ask then ask at check-in for the cruise account to be kept in Dollars.
Alan & Katrina
Last: P&O Oceana December 2016
Next: NCL Jade August 2017
Then: P&O Ventura December 2017
Golden, Grand(2), Caribbean, Royal, Sea(4+1 aborted)
Adonia(4+2), Arcadia, Artemis(2), Aurora(5), Azura(2), Britannia, Oceana(4), Oriana(12), Ventura(2), Victoria(5)
QM2(2), QE2(9), QV(7), QE, Caronia(2),
Oceania Nautica, Minerva, Minerva II, Fred.Olsen(8), NCL Jade, =X= Eclipse, HAL Ryndam, Aza.Journey, CMV Magellan