I applied for Cambridge last year (I had 3A*s, 6As and a C- the C was in Drama), my AS grades were okay (an average of about 84% overall). I applied for Natural Sciences and I got an interview, I didn't get offered a place but that was probably because my interviews didn't go too well, more than anything.
One of my friends applied for Engineering at Cambridge, she got 10 A*s and As at GCSE (she got more A*s than As), however at AS level she got AABB (after a remark it went up to AAAB) and she didn't even get an interview.
So I would say that if you aim for about an average of 90% in your AS levels (these are much more important in your application than GCSEs), and write a killer personal statement, then your GCSE grades won't matter as much- especially not the D in Drama as that isn't relevant to Law.