I didn't get the perfect set of GCSEs but I didn't do too terribly. I know that A levels and UCAT are the priority but GCSE grades are used too.
My GCSE grades:
Combined Science: 9-8
Maths: 8
Spanish: 7
Enterprise: Level 2 Distinction / 7
Hospitality and Catering: Level 2 Distinction / 7
Geography: 6
English Language: 6
English Literature: 5
For A levels, I am aiming for all A* in Biology, chemistry and maths and I'm also doing an epq which I am aiming to get an A/A* in.
I don't know if this affects my chance but I'm hoping to do the Stem Potential course at the Imperial College during my A Levels.