The guidelines for the GCSE and A-levels has now come out.
assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/877842/Summer_2020_grades_for_GCSE_AS_A_level_EPQ_AEA_in_maths_-_guidance_for_teachers_students_parents.pdf
Main points, schools will come up with the grades using their professional judgement and performance in exams, assessments, in class etc...
They will then rank the students in each grade band.
This will then be subject to statistical analysis by ofqual and might be adjusted.
The results will be published ahead of the usual schedule and certificate will look exactly the same as any other year.