I've just been looking at the Disability Discrimination Act's definition of disability - "a mental or physical impairment which has a substantial and long-term adverse effect on their ability to carry out normal day-to-day activities".
Now obviously a nut allergy is not the same kind of disability as a life-limiting illness or MS. And it may fit the criteria, I guess depending on how you define "substantial". I haven't made up my mind. Just wondering what others think.