Bsc need 150 points, Credits; Achieved = 2 points, Merit = 3 points and Excellence = 4 points. If you're grades are high enough (And I would say surpass), it should be fine. Although University would prefer it if you have done Level 3.
A friend of mine who was a year behind got into Biomed instead of 7th form, she was insanely intelligent and hardworking.
Do 7th form, it's good. I was initially considering moving away from school at 7th form, but decided otherwise. I don't regret it, I was never good at school per say, but it was a very enjoyable experience. Teachers treat you on par, ever the grumpiest Head of Department.
Have you done Level 3 papers?
If you really want to min-max, save up the money required. Keep term depositing it until you've finished university, afaik there's no interest nor set up fees for student loans. Just don't spend it all on booze. Once you start uni..what else would you spend your money on?!