your fic should (and from what I have seen from being ~15% in, will) push a LOT of the right buttons for me. I have a thing for the particular flavour of AU you're writing here, and it seems reasonably well written so far.
However. I keep being thrown out of the fic (yes, at only ~15% in) by the fact that you keep calling Character A, A, even though he introduced himself as B. The physical description, nevermind the plot summary, made it clear that it is A, so until A himself, or another character, reveals that his real name is A, please refer to him as B. Even if another character, upon being told his name is B, doesn't believe that B is his real name. We haven't had any POV from A yet, so ought not to have any way of knowing that A is in fact his real name.
Trust your reader to know that he's A, using B for a reason for now. And find other identifiers to use in action/description/speech tags, etc,. You're clearly good enough to make things like 'the brunet'/'the shorter man'/'the job title'/'the age differential identifier' etc work.
p.s. I'm not saying you need a Brit-picker, but: Britain=/=Briton. Briton/Britain/Great Britain/United Kingdom all mean different things, and now I'm really thrown out of the fic.