Just a medical view for what it is worth. The UK CAA flowchart is sensible. It states if you have a historical allergy and have since been exposed but had no reaction there is no restriction. This is most likely a misdiagnosis or desensitisation as an allergy is a learned abnormal response of the immune system and once programmed rarely goes away other than at puberty.
The allergy report they require is simply the trigger or allergen and the severity of the response
If an epipen has been prescribed you are limited to an OML
However, asking the consultant to provide a report "An anaphylactic risk, as a percentage per year, if exposed to the allergen"? is medical mumbo jumbo!!! If an individual has a true current allergy there will be 100% risk of a response on exposure. The issue is whether the individual can avoid exposure whilst flying.