Most colleges ony require two B's in double. Mine did. Good job on choosing physics the subject of the kings. If the requirements for physics are A at your sixth from i'd be a bit worried that a school which get **** grades as you put has such high requirements. Most likely on enrolment day they wil allow you to continue with a B as they tend to do at my college does well for an inner south london college. Especially if they're starving for students in physics which appears to be the case.