Rikesh - in your first 2 years you would have time to do a couple of hours flying per week definitely. The only problem with this is funding it - 2 hours per week @ £130 = £260 per week. If you already have the money then go for it ... but you won't have time to work in order to save that amount.
I'm not really in a position to be offering career advice with regards to maths a-levels and degrees. However, as a guess I'd say that a maths degree would open lots of avenues down the road and wouldn't leave you unbalanced. Then again, if I were you I'd go and speak to a careers adviser (about maths - they tend not to know too much about aviation careers). There should be one at your school/college.