You first question was "what the average successful applicant is
predicted"; this was in relation to UCL. Your second question was "what the typical successful applicant
has"; this was in relation to Imperial. What a student "has" (i.e. achieved) and what they are predicted to achieve are clearly different.
According to TheUniGuide, who get their data from HESA (Higher Education Statistics Agency), the "Most popular A-Levels studied (and grade
achieved)" for Biochemistry at
UCL are:
Mathematics: A
Chemistry: A
Biology: A
See
here.
Another source is DiscoverUni, which provides entry information in terms of bands of UCAS points. This is a flawed approach as students can gain UCAS points from qualifications which UCL could completely ignore (AS levels, EPQ, Grade 8 Violin, etc.). However, that data (from 55 students starting 2018 - 2020, using data collected directly from universities and colleges) for BSc (Hons) Biochemistry at UCL says that:
2% had fewer than 48 points
4% had 48 - 63 points
2% has 96 - 111 points
93% had 144 points or above.
(The number don't sum to 100 due to rounding). AAA is 144 points. See
here.
The equivalent data for Imperial is in those same sites.