You're forgetting a protracted battle with the middle east + a big fuel shortage (no Oil)
COUGH COUGH FISSION POWER COUGH COUGH
Ships float, they can be as heavy as they bloody want to be, they could make NUCLEAR FUSION powered ships, the fact that it is possible to have NUCLEAR FISSION... You could have some MEGA battleships with that power...
Not to mention they are active in water, Fission uses hydrogen, water... + electric current = hydrogen... Unlimted fuel?
Britain I believe would cope because;
She has already had experience with total war and survived.
Her sea power is almost impossible and EXTREAMLY expensive to destroy with nuclear missles.
She could lose her army in the Resource war, but she would still have her navy and that would stop a landing.
After the bombs the majority of her land would be wasteland but she would still have a huge navy just floating around.
Which begs the question why they havent show up in America... Maybe they were clever, Aftrica wouldn't have been bombed...
Maybe Britain after the war sailed her huge fleet of warships to Africa and now there is a single Super Power rebuilding her Empire with the Non Radiated parts of the world...
Ooooo I like this idea....