There are good nursing schools in London. And US based school loans will cover the costs of schooling overseas. the big pain in the arse is your visa - which you have to give enough time to get (check out www.state.gov
for more info on living abroad). Do a "google" search and a few pop up. As well in the US, I know Case Western Reserve Univ (in Ohio) has an affiliation with the WHO and student nurses can do a oversease rotation with the WHO -- or take part in their research projects. I also know Georgetwon Univ offers and international health certificate in conjunction with their nursing program, so that might be an option as well.
But be careful, if you want to practice in the US, you may need to retake classes (depending on the state). I have heard of UK trained nurses/midwives with tons of expereinces having to re do classes/degrees in VA.
Have you thought of doing the Peace Corps after you earn your degree? Might be something to consider. I did (not as a nurse, I went after my first degree). They cover all your travel expenses, you have a great expereince, and you can do some amazing things! This might be a good alternative to going as a student nurse -- as with peace corps there is no cost involved. www.peacecorps.gov