How do mitigating circumstances and Clearing work?

If you've been rejected by your firm choice, what is the likelihood of you being accepted onto a Clearing course with requirements lower than your firm choice but still higher than the grades you got in the context of these circumstances?

I ask because typically the places you've firmed and insured are supposed to be more accommodating in such situations. How should that phone call on Results Day work? Do you communicate your grades, and then say that you can provide the evidence for the circumstances by email? Should you have the evidence at hand to communicate details they may want over the phone?

Is it even worth contacting unis through Clearing? Unlike the five unis that you applied to and firmed and insured in the first half of the academic year, your Clearing choices obviously don't have your predicted grades, references, academic record and personal statement at hand. And because of the way Clearing operates, you can't fill out their mitigating circumstances form/complete their procedure ahead of time - you haven't built the rapport that you can with places you've applied to. Do these factors mean they'll be less likely to be convinced? What would you do?

Yes, they do. When you are in Clearing, universities have access to your complete UCAS application. That is what having a Clearing number allows. Therefore anything on the form which was communicated to your original 5 choices via the UCAS form will be equally visible to the clearing universities. When you apply for a place in Clearing, you are talking on the phone to a real human being, so you can tell them what other evidence you may have submitted to your original choices and they will deal with that knowledge in exactly the same way as the first places you applied to did.