I know my school have already ranked their students for most subjects as they have plenty of data. They are trusting the heads of department to give the grades as well, keeping in mind the school’s previous performance and the ability of this year group. The teachers know the students well and their backstories, ie those who have extra time or have been working hard recently etc. Obviously adjustments might be made once the detailed guidance is out.
My own DS goes to a different school and doesn’t do physics and I am very relieved about that, avoids any potential bias or extra worry.