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Further Maths in my Gap Year

Currently I'm in A2 studying Maths, Chemistry, Economics (dropped Biology AS)
I am in the process of applying for universities for a Masters in Maths Course [MMath]
My predictions:
Maths: A*
Chem: A*
Eco: A

Problem is most good uni's require FM at least to AS, now seeing as I'm doing Maths A2. I thought I'd apply for sake of applying to uni's like Bath/Bristol which say FM isn't a complete requirement and get offers from them hopefully.

But if I were to get my predictions (A*A*A) I would consider taking a gap year, furthering my extra-curricular Maths knowledge and doing FM A2 in this gap year and complete the exams by either Jan or June 2014.

Cutting to the point, I want to know when I'll apply to these uni's (hopefully Cambridge), being done with A-levels at school who will give me my predicted grade for further maths and how does this process really work? Will I still get an offer for 'saying' I'll self-teach myself FM in my gap year?