If you're looking to get an 'A' at A-Level Economics I would suggest using the materials from
http://tutor2u.net/ which helped me a lot at during my A-Levels.
Also, if you're looking to get into the best university possible I would recommend dropping business studies and picking up one of the more 'traditional' subjects (e.g. History, Physics, English, etc). Bonus points if you can pick up further maths too.