Re Australia: I can give mediocre advice by relation to the figures at Nottingham, but it should serve as at least some level of guidance. Looking at those, and the sheer cost of USA, the Australia will be very competitive. We too apply at the start of second year, and can apply to Australia (melbourne, sydney, queensland), New Zealand, HK, USA (texas, virginia), Singapore and China (As of next year). I know for a fact that Australia is always the most competitive... and without the other options on the table, it is going to be very very competitive to get onto that at KCL.
However, this is no substitute for the direct word of the tutors involved. But jsut to warn you of how hard it will be. Australia is everyone's favoured choice because it's just a year in the sun!