I think it's possible for you to get into university to do music. It would really help if you did A-level though; it tends to be a course requirement. Maybe if you explain that you need to do it to your school, they would make an exception. I think some universities ask for Grade 8 theory if you haven't done A-level.
Just as an example, Edinburgh University (in the top 20 for music, and top 15 overall) asks for: a standard equivalent to Grade 7 in your first instrument, a standard equivalent to Grade 5 in piano/keyboard instrument, BBB at A-level and Music A-level at B. Most other good universities
are higher than this though, but it does show that getting in is within the realms of possibility. No offence to above posters, but you don't
need to "forget about reading Music at university" - you could do it. They don't all "tend to be AAB" either, by the way; according to UCAS and various prospectuses, Bristol is ABB, Durham is ABB (but offers are often lower), Cardiff is BBB, Leeds and Sheffield are ABC, Newcastle is ABB...and they're good universities!
Obviously there are various requirements as to what grade you have to be too, but you getting Grade 8 is eminently attainable, especially with a gap year.
Do kick up a fuss about doing A-level; if you're serious about studying Music, get that A-level any way you can. I mean, I know I could pay a bit over £1000 and do it privately in the local music school if I wanted, and I'm not even in an A-level country.
Good luck! (And remember that music is something that can be a huge part of your life without having to study it.)