Well, it won't affect you massively (not being able to get a decent job for example), but it will definitely limit your chances of getting into a top or a normal college as well as university. Also, it will affect you greatly if you are planning to carry on, as someone has already mentioned above.
If you get low grades on those, then you will get less points overall, meaning that you won't be able to do many A-levels.
I'm guessing those are your options for your GCSE?