For the point about double science- I did double science at GCSE and was thinking the same thing two years ago. IMO it didn't matter at all if you did triple or not. As long as you understood what you learnt in double science, then your really at no disadvantage. Everyone is taught the same course content. For the first 1/2 weeks in chemistry we were just going over gcse stuff anyway and then we started to learn about mole calculations- Triple science covers topics like these more than double science, so often people say you are at a disadvantage but from my experience most of them had a pretty superficial understanding from gcse anyway and so everyone was pretty much on the same page when learning in class. I did maths, phys and chem so can't talk for bio but I would be surprised if it was any different...