music a-level without grade 5 theory?

If you're Grade 7 violin (Trinity, I assume?) then why don't you pick up some theory workbooks and work up to Grade 5 standard yourself? You don't have to do the exam, but if you're interested in music, why wouldn't you want to learn the theory anyway? It will only help at A Level (which, in response to your question, is probably okay without Grade 5 theory, but you'll have to get your head around harmonising Bach chorales, so you might as well do the Grade 5 stuff to give you a solid base).