One of the great ways to learn a language is to emmerse yourself in it, spend time amongst the natives and soak it up.
Easier said than done when your language of choice is Japanese and you live in the UK. So rather than give up, here's a way to do it: www.splume.com.
This is an emmersive online world much like Second Life, but aimed at the Japanese market and, apparently, following a somewhat different design philosophy. Whatever, I'm sure it would be fun.