Yeah, first thing that came to mind was LSE Actuarial Science. From what you've said, I think you can do better than Southampton, which is good but by no way means great, but the problem is not many top universities offer Actuarial Science. You might want to try applying for Economics and then becoming an actuary or doing something like Maths and Economics, MORSE, Mathematical Finance etc. Basically courses that will give you a good preparation for becoming an actuary.
So, from what you've said I'd say that you can do better than Southampton. Obviously apply to LSE for Actuarial Science but for the others, you might have to apply for Economics or a more mathematical version of it, because Actuarial Science is a specialised discipline which few universities offer.
I could probably make some more detailed suggestions, but I'd need a bit more information. Could I ask what your GCSE and AS grades are and in what subjects?
Hope this helps,
Sen