As a preface, Japanese degrees in the UK usually see the student spending 50% of their time learning the language and the other 50% of the time studying the academic side of Japanese studies (including politics, literature and religion etc). Of course, the split might not be even in every university, and the standard of the language as well as the academic education will vary from institution to institution. In any case, here are my thoughts on the Japanese degrees offered in British universities (from what friends who've studied Japanese at the following institutions have told me and my own speculation):
Oxford - Extremely heavy emphasis on history, literature and classical Japanese language. Might not have the best command of spoken Japanese but knowledge of grammar and ability to read will be great. Furthermore, all students go to the same university during their year abroad (unless they've recently changed it). I understand they might do this to maintain academic standards for their students while abroad, but it completely holes them up in a bubble. There's a high chance the students just end up among themselves and not really speaking Japanese while in the country. Ergo, go here if you want to learn more about the academic field of Japanese studies (and might want to do a PhD in the future), but not necessarily if you want to improve your conversational Japanese. That said, even though I say that Oxford hugely focuses on the academic side of things, that doesn't mean that your spoken Japanese will be bad; in fact, it'll be amazing (and very advanced) but perhaps not as conversationally fluent as those studying at SOAS or Edinburgh.
SOAS - phenomenal for language students. However, extremely, extremely competitive (and, to an extent, toxic) student community. Huge focus on reading, learning kanji and passing tests. Everyone knows everyone's grades and is vying for top place. Every man or woman (or otherwise) for themselves. Speaking will improve (and most likely be better than an Oxford student's) but still a little lacking due to the heavy emphasis on test-taking. My friend who graduated from SOAS in Japanese also mentioned some terrible things about SOAS as far as departmental politics go. I'd recommend going here if you really want an extremely competitive atmosphere and to receive the most rigorous Japanese language tuition (SOAS students always score the highest in written placement tests at Japanese universities).
Durham - extremely new Japanese department made only a few years ago. Don't know anyone who went here but would most certainly not recommend going somewhere where they've literally just begun the course. Even courses which have been going on for decades still haven't perfected the formula, especially for a course as difficult and sinuous as Japanese. Although I realise that I'm being frightfully presumptuous and biased against Durham, I just know (from experience) how painful university bureaucracy is. As a general rule of thumb, avoid new courses/degrees/departments (unless you hear wonderful things) because otherwise you'll just be treated like guinea pigs and set up for failure.
Manchester - Very respectable university with an impressive international brand. That said, the uni itself receives poor ratings for student satisfaction (as most big universities including Edinburgh do) and, surprisingly, its Asian Studies department seems to score rather low as well in contrast to Edinburgh's (which is near perfect). This isn't a great sign, so I'd be cautious... They also have links to some of the most random Japanese partner universities: from the elite of the elite to some of the complete worst and unknown Japanese universities. I, admittedly, don't know too much about the actual course but a few of the guys I met during my YA didn't speak it too well (could be just them). Even so, I imagine their Japanese reading ability was better. In any case, Manchester has access to its interpreting and translating department/s, so I imagine there would be some very useful modules in that. All in all, I'm not too certain about Manchester, but the very little that I have heard has made me unsure of the Japanese degree there. On a positive note, there was a current student of Japanese at Manchester who used to frequent TSR and her experience had generally been a positive one so far (she was in 2nd year at the time).
Edinburgh (long section because I can give my own personal account) - excellent language courses with heavy emphasis on speaking. Reading, although covered in depth throughout the degree, is perhaps not hammered in as much in the first two years as the SOAS or Oxford Japanese programs. Ergo, JLPT test results (which don't examine speaking ability) in the first few years might not be as good as SOAS and Oxford students' but will generally even out during the year abroad. Speaking, on the other hand, will be of a higher standard.
Partner universities are also being cut down to about 6. Even though they're all elite universities, you'll have fewer options than the previous lineup of 12+ (that I had when I studied abroad).
Edinburgh is also heavy on academic Japanese studies (but not as much as Oxford), so you'll spend 50% of your degree studying Japanese/East Asian history, politics etc while the other 50% will be spent studying the language. The academic side can be dense at times and some lecturers are somewhat dull. The department is definitely carried by its exceptional language classes and tutors. I'd say that the language staff are the heart of the department as the environment is extremely tight-knit and you'll be friends with everyone up to 4th year, the language tutors/lecturers as well as all the previous senpais who've already graduated.
The Asian Studies department (including Japanese and Chinese) always gets exceptional reviews and ratings even when the university as a whole struggles (as most big universities do). I've actually heard nothing but rave reviews about the Chinese Studies department. What's more, every single academic lecturer for Chinese Studies is amazing. I was very pleasantly surprised and hooked in all my lectures of modern Chinese history!
As an aside, in your first two years, you can also take an outside subject. So, you would generally do: Japanese language + East Asian history etc + 1 more subject (in practically anything, as long as there are no timetable clashes and you meet the requirements like having A level Maths for a 1st year Maths course). You can also change your degree to your outside course if you want. In other words, if you did Japanese language + East Asian history + Economics in your first year, you could switch to an Economics degree!
Cambridge - no idea whatsoever.
Leeds - have heard nothing but great things about here and their Asian Studies department (which is very well established). Leeds is also a lovely student city. Potential major con (or pro) to studying Japanese at Leeds is that they send their students to Japan in 2nd year. I'm not convinced that sending students to Japan at a post-beginner's level (the level you'd attain after 1st year) would see them reach advanced stages of the language after a year. In other words, sending students in 2nd year lowers the skill ceiling that students can reach. Generally, everyone improves their language abilities the most during their YA, so sending them at a higher level means that they can become all the better; but, sending them at a lower level, although helps them improves rapidly, lowers the ceiling. They'll probably come back post-intermediate whereas students going in 3rd year go as either intermediate or post-intermediate and come back advanced.
This is either good or bad depending on how you view this.
Sheffield - have heard quite decent stuff about here. A friend who graduated from here in 2016 said that some of the courses weren't too intensive as she had hoped, but I've also heard from a student on TSR recently how the courses are intensive. In other words, I'm not really sure but since the student on TSR graduated from Sheffield recently, I imagine the Japanese degree at Sheff has probably changed a little over the past few years and has improved quite a bit.
Oxford Brookes - 2 Master's students at Edinburgh who had done their undergraduate Japanese degrees at Brookes praised the university but did admit that they felt some of the content was a little too easy to pass at times (which doesn't sound too bad to me...).
UCLAN - In all honesty, don't know a single thing about here since I don't know anyone who's studied here or any member of staff teaching here (unless they've recently acquired someone I know).
Final note
Think carefully about what you want from your Japanese degree. Whether you might want to go into academia in the future, want a well-rounded education or just want to stroll by. Moreover, look into the academic Japanese studies modules offered at each university because 1) every Japanese studies department has a completely different focus and 2) at ancient universities like Oxford and Edinburgh, you'll be taking half of your courses in this. While Edinburgh's focus is more on contemporary societal issues, Oxford's is classical, and SOAS is more general history (and, perhaps, linguistics?). Finally, consider the location as London, Manchester, Edinburgh, Oxford, Durham, Leeds, Sheffield etc are all very, very different. The year abroad options offered by each department are also equally different.
All universities have their pros and cons. In all honesty, you can't go wrong with any of the universities. You just need to be aware of what you'll be getting yourself into as every department has its own focus and way of doing things (like Leeds sending their students abroad in 2nd year while all other universities do this in 3rd year).
If you want more information regarding a Japanese degree, here's another thread I've posted on: