Great question — answering as the UphillTech team:
After asking a few establishments I received generic* answers about the letters denoting the type of allergen (e.g. type of nut - peanut, walnut, etc.). I was never provided any specific answers, like 8d meaning the food contains peanuts, so I don't know if there is consistent meaning or if it is establishment specific. *Without a common language between us communication was limited.
Full answer by redmaw: https://travel.stackexchange.com/a/191630 (CC BY-SA 4.0).
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