[MMM]

How would you advise I go about learning the language? Self-study clearly hasn't been working for me, but I have learnt the very very basics, and have learnt hiragana and katakana and some kanji (I found a great book that teaches kanji but I need motivation to get on with it). Would a full Japanese course here or a language school in Japan be worth the money?

I think your money would be better spent living in Japan and learning more through osmosis than taking a class. You have a university degree, so you could apply to JET or other programs to get placed in Japan.

What level of language proficiency would I need if I did decide to study in Japan? I know some universities offer a 6 month pre-course to help with language but obviously that isn't enough time to learn the language.

In Japanese? Better than fluency. I wouldn't recommend that path.

Having learnt the language how hard would it be to get a palace on a masters course at a good university in Japan? And having got the degree how well recognised would it be outside Japan?

I have been a student of Japanese for about 20 years, and have been a professional translator for 5+, and I wouldn't dare imagine I could get a Master's degree in Japanese language. There wouldn't be enough hours in a day to read, write and keep up with my studies, even if I didn't sleep.