I'd be interested. I'm in the planning stages of my own post apocalyptic YA, so we could talk genre issues like, "How will they get electricity?"
Mostly kidding. The very last part of your first chapter really drew me in, and I think that I must, must know why these parents are going on holiday when the world is ending.
As for me, I'm an American as well, so I don't know how much help I'd be on the British front. I teach high school English, so I'm pretty good with finding any errors you might have missed. I also love YA fiction.
How about you? What kind of time frame are you looking at here? When would you like your betas to have the book read and back to you?
(I'm also a bit new to this beta thing--I expect you send the manuscript in electronic format?)