Mischiefinthewind I remember that years back when I was teaching secondary too - none of the kids in my tutor group had food allergies listed.
I brought in a big box of celebrations or some similar chocolates to share during tutor hour at the end of term. About 1/3 of the class piped up claiming nut allergies - obviously this seemed unlikely, they were all free to pick out nut free chocolates but I warned them that if they really had a nut allergy they should not take any chocolates, because there was a high chance of traces of nuts in any of the chocolates, as they were made in a factory which used nuts and packed together.
Cue a round of "oh its not a really bad nut allergy, I just can't actually eat nuts..."
When the box did it's third round of the classroom and only nut containing chocolates were left even the mild allergies cleared up in most cases and most of the kids helped themselves to something with nuts in it rather than nothing, and nobody showed any ill effects.
Obviously none of those kids had nut allergies, because if they genuinely had it would have been on the priority information board in the staff room (there were a couple of kids with genuine allergies up on that board, with photos and descriptions of allergies so that in a big school all staff would know about it).
They still tried it though - I guess many of those kids I'm picturing are parents themselves now actually as they were year 8 about 15 years ago...
I remember a girl I was at school with myself 30 years ago trying to claim over a period of several weeks when she first joined the school that she was allergic to water and had to be given squash with her school lunch - she was 12 or 13 and old enough to think that through and see why nobody believed her...