You can use Uniguide (and now UCAS) to see the actual grades students who got on the course actually achieved - just google it
Some (many?) unis will be a bit flexible but it depends a lot on the courses / applications that year - if they can fill the course with applicants who meet standard requirements then they wont accept a missed grade (e.g. my daughter was rejected from Bath with ABB after firming with them at AAB)
It might not be true but, talking to admission tutors at Open Days it seems they do prefer the firmed students over the insurance students, which is good for you
Do you have a Plan B? Having an insurance choice you would equally like to go to takes off some pressure. Doing a bit of research in to Clearing (just in case) also helps you to have Plan C
FWIW, in case you don't know, on results day you will get the Uni decisions through UCAS quite quickly (Unis get your results a couple of weeks before results day) when UCAS releases everything. So my daughter found out Bath had rejected at the same time she found out her insurance accepted her
Reason I am here (Liverpool forum) is my youngest looking at Liverpool for BioMedSciences and is a bit concerned about 1 of here subjects