If it's not listed as required or preferred you should be ok. It also depends which uni you're applying to tho, as you might struggle on a maths degree w/o fm even if you do get accepted.
I was in a similar situation where I wasn't sure whether to do MORSE or pure econ. I asked at the open day about doing MORSE w/o fm and they said I would likely struggle since they don't teach it from scratch and assume everyone knows the fm content already (this was warwick uni) so I ended up applying for econ. I'd advise you to check this with the unis you're applying to (some teach fm stuff you need from scratch, some just review it quickly in a few weeks)
Maths+Stats would prob be more difficult, it might be worth learning some fm content in the summer of y13 if you decide to choose it.