Data Science BSc Competition (UCL/LSE/Warwick)

I'm interested in pursuing Data Science potentially at one of the above universities (likely Pol and Data Science at the LSE). But, I wasn't sure on how effective of an application I can put forward with:
- My very tame GCSEs (1 9s, 4 6s, 3 5s), which were all TAGs.
- And just A-Level Maths (not FM).
I do take 2 other preferred subjects, however. Could people comment on if I am required to resit any GCSEs and how that may look for the likes of Warwick/LSE/UCL. I'm not sure how it will affect my exams at A-Level as i'd probably have to retake 7 GCSEs concurrently.
So I'm wondering the following:
- Can 7 GCSEs be retaken successfully along with A-Levels,
- If so, is the payoff worth it to retake GCSEs (if I spend money to retake and then they say that, well you got them 2nd time around and others did not)
- If it is realistic to apply here offering only A-Level Maths