Although, I haven't taken Math for my A-levels. I strongly suggest that you shouldn't do M2 in Jan 2012.
First of all, you have 3 papers in Jan which trust me will be more than enough.
I assume you are doing Chem 4, Phy 4 and C3. . .yes ?
Trust me, M2 will just be a burden on you with the rest 3 hanging along yer shoulder too.
God forbid but you don't wanna ruin yer grades in the rest 3, right ?
Just concentrate mainly in these cos they are vast and require lots of practice.
I advice you do M2 in June 2012, Insha Allah. (:
May Allah guide you to choose the best/right choice, Insha Allah.
Good luck. (: