Predicted grades are typically higher than achieved grades. If a course is heavily over-subscribed, the admissions team might opt to only make offers to candidates predicted A*A*A or above. The offers would then be at AAA or A*AA, which most of these candidates would attain.
I have no knowledge of what Imperial do for Biotechnology. I'm just aware that knowing the typical / standard offer isn't always particularly useful when assessing how likely you are to receive an offer.