I don’t think you can bank the CCC for insurance can you, as effectively it is conditional on firming (I think).,,
No, the attainment offer can't be used as an insurance. I meant, if it's putting one's DC off, even if only the one thing which is, then having the university as insurance takes away the disincentive of knowing that they have the temptation to get sub-optimal A levels, but still offers the opportunity to go to a university that they liked otherwise, iyswim. But that's not a lot of help, either, if the normal offer is higher than one's other options, of course...
Seriously, if I would like to firm Birmingham, for the university, location and course, I would go ahead and do it, try to put the safety net out of my mind and if necessary, put sticky notes everywhere with, Remember you need AAA for Birmingham or whatever on them and carry on working
.