Hey,
My A Levels were only slightly better than yours (ACC) and whilst I did finish a degree, I didn't exactly blow anyone away with the results. Also doing a HE Diploma, don't even have any 'Graded' units back yet, but I've got two conditional offers from Manchester and Bristol, both pretty top-tier universities.
Not at all trying to brag, simply to show that... well, what you've done since education and how you apply yourself to your HE Diploma is much more important as a mature student, and you can certainly get into very good universities through it. You can do it! Good luck!