The grade boundaries are:
U-<30%
F-30%+
E-40%+
D-50%+
C-60%+
B-70%+
A-80%+
A*-90%+ (not available at AS-level, only A-level and GCSE)
Only grades A*-C are recognised as a pass. As for my GCSEs, I got 3 A's and 9A*'s.
I've only just started the AS-level courses in September, and a B on my first practise paper isn't too bad. Mans three of my four subject teachers told me I'm predicted to get an A in the summer, so miss me with that bullshit.