any uni asides from oxbridge, Durham and possibly LSE doesn't care about gcses even then if you have amazing a-levels e.g. 4A*s you would have a good kick at getting into pretty much anywhere, if you have a-levels which aren't anything special and hit the required grade for a course, e.g. applying for a course with AAA which needs AAA, then extra currics and other qualifications will be used to differentiate between candidates