I'm not sure that you can get into such a competitive course with just 7 GCSEs, no matter how good your A-Level results are. I thought I was looking at a list of A-Level results orginally (you didn't specify until the end of the post), and even then I was thinking it would be better to push up the Maths and English Literature grades anyway.
The application is, I believe, mostly based on Sixth Form results, but you definitely want more than 7 GCSEs, even if a couple of them will be B's. The rarity of applicants who do so few GCSEs means that, for instance, someone with 7 A*'s will probably not be valued as highly as someone with 4 A*'s, 3 A's and 3 B's, simply because the officers just aren't used to seeing people with so few GCSE subjects. :P