As an undergrad I was in a similar situation. I had both Spanish and Latin, but my ability in both was rather poor. As an MA student in the states I had to complete a reading proficiency requirement which I chose to do in German. I had no formal classes in German to speak of just independent study and some time spent in Berlin, but in one semester I was able to read academic German fairly well. (with the aid of a dictionary of course.) For German I really found Jannach's German for Reading Knowledge extremely helpful. You can also find books that teach you principles of other languages via principles in that language, which I think helps because you make that connection. That said, I don't think I could have progressed as quickly as a I did without a classroom setting. My instructor really pushed us and I do so much more German than anything else, but it paid off. I'm not sure how the system works in the UK, but perhaps you could look into taking a certification course offered to MAs at a nearby university or college. You may not get credit for this course as you wouldnt be an enrolled, degree-seeking student but you could get your reading ability up to a good level. Good luck!