I'm in a similar position. I need ABB for my Chinese Studies course at Leeds and I'm sitting on BB at the moment, with a few exams next week (I'm retaking History on Monday as well coincidentally). I don't know an answer for sure, but a lot of it is based on luck. It really depends on the grades other applicants get. If every other applicant got the required grades and you didn't, you probably won't make the course. If a large percentage didn't get the grades, you'll be a lot more likely to get in. It also depends on how many applicants for the course there were. There are other factors of course. They'll look at your references and your personal statement for example.
Going on what I've heard (again, I don't know for sure), I think there's been less and less university applicants generally recently, so there might be more spaces available these days, which will improve your chances. A lot of my friends who are already at university dropped a few grades here and there and they still got on to their courses without any trouble.
Best of luck!