That's a very big question, and not one I'm really qualified to answer. But strictly in technical terms, there are a limited number of transmitters in the UK, and a limited number of slots available on them. So even if the BBC was minded to make all its programmes available everywhere (over the air in the traditional way), when you look at it from a straightforward transmission point of view, its probably not possible (but I'm not an authority on that by any means). However, given the worldwide availability of Listen Online and iPlayer, pretty much everything broadcast by the BBC is available online nowadays. I appreciate that's not the same thing as listening on a traditional set, but it's a start.