So at the shop today, I made a random purchase of some UHT milk for the first time in ages, from the back of the shelf where I thought it would be less likely to be poisoned.
When I got home I had a tiny taste test, a little sip, just a drop, then almost immediately I started getting a (slightly) sore stomach, I know through bitter experience that I would be in agony if I had some cereal or something like a normal person, so down the drain it went. I am not allergic to milk by the way (only poison) if it passes the taste test, I can drink it as normal.