Over the past few years, PE has been growing in popularity eg about 5 years ago just over 10,000 students did it - this year almost 13,000.
In particular, we are now attracting plenty of top students who recognise it's value to gain entry into courses such as medicine, physio and radiography etc etc
With more people doing the course, and also more really talented students the scaling is getting better and better. I don't think they publish scalings anywhere public - but the consensus is that PE scales about the same as Biology.
If you do well in PE (like any other subject), it will really help your UAI.