It depends what course and where you are applying to for how competitive it is, however the majority of business courses arent that competitive. Just get the best grades you can, explain in your PS how doing this degree will help you in what you want to do, and get work experience in any field (I did an architects office, a primary school and admin in a drilling company). To be honest thats more than enough!
your A Levels dont even have to be that relevant, I did English Combined, Art and Communications, and I have had an offer for the marketing course at Northumbria which is pretty popular. Just make sure they know that studying the course will help you get to where you want to be