I think your research is way off there. The average accepted Cambridge candidate is going to have way more than 4/5 grades 7-9 (A or A* in the old money) at GCSE.
Medicine applicants are very likely to have all 9s in Maths/Sciences at least. I know GCSEs aren't the defining factor for admission, but unless there's some heavy context or you have all A*s predicted at A level (which will supersede the GCSEs) then you'll struggle to get an interview with those grades, unfortunately. Same with Imperial which is, if anything, even more competitive than Cambridge.