The QAA provide extensive guidance on how Access to HE Diplomas are graded.
Grading scheme handbook: Index
Grading scheme handbook Section A: Introduction & Summary
Grading scheme handbook Section B: The Grade Descriptors
Grading scheme handbook Section C: Using the Grade Descriptors in Assessment
Grading scheme handbook Section D: Moderation & Standardisation
Grading scheme handbook Section E: Students results and awards boards