One on one, who wins? And I mean it when I say 1v1. That means no colonies can come to their aid. Not adding a poll because I know the biased Brits of this site will be biased and vote for themselves without coming to any logical conclusion on why their country would win.
Neither France noir Great Britain have the capacity to invade each others, because they don't need it. Nuclear capacity is the heart of the defense of the both countries. If Great Britain had no armies, no aircraft, no ships but the nuke, a lot of nuke like they have, no one could defeat them. Imagine a great scale war with France and GB without taking considaration of the nuke is like imagine a fight between medieval knights without armors and sword : pointless.