Make sure to clarify the visa situation too if you're doing this on your own rather than through some exchange program (which I don't think is the case, as your mentioned doing you entire A levels over there. I think there is pre-college student visa, but the school has to be willing to apply for it so make sure you ask them for it.
Also there are plenty of A levels school in most major cities in the world. I know there is British Intl. school in Tokyo but its horribly expensive.