GCSEs don't particularly matter. Well the subject choices at least. As long as you have good grades in Maths, English, Dual award (or Triple Science) and other subjects. They may ask for a certain amount of A/A*s or A-Cs.
As for A levels, you'll have to look at the entrance requirements for the various degrees.
I know for Medicine, most places will want the complete Chemistry. And a lot will want Biology to at least AS level. Cambridge ask for 3 science A levels but they're the only ones.
The list of Medicine A level entry requirements is here. That wiki also has other info that a prospective med student will be interested in.
Medicine is a 5 year degree.
Other Bscs, such as biochemistry, are 3 years. While you have to have a medical degree to be a pathologist, you can work alongside them in other roles by undertaking another life sciences degree and then doing the appropriate post-grad training. I've had a look and quite a few bio-science degrees require Chemistry and at least one other "hard science".
So Chemistry, Biology and 2 other A levels would be a good AS level combo in my opinion. But you've got to do your own research and figure out what's best for you
. Personally, I took Maths, Further Maths, Chemistry, Biology and Music and am aiming at a Medical degree.