Think you're aware it won't be quite as easy as someone who had done a more 'aligned' degree but it wouldn't inhibit you from getting through the exams.
You would have to start from scratch with the certificate level ut that would give you a good grounding for the rest of the course and you would just need to ensure you put the work into studying otherwise it becomes difficult. Obtaining a degree gives strong indication that you would be capable of completeing the syllabus. I personally had a Law degree and am just moving on to the Strategic level, and very little of what i learnt is replicated in CIMA but CIMA is set up assume no prior knowledge.
I wouldnt get het up on the A-Level, good maths skills help a little, but you can just put a little time into particular areas. I would say brush up and practise some basic maths though as i found that helps massively, like quick additions, mental arithmetic, percentages etc - these help in the exam and people dont often look over these areas.
