A Testing Chip
There have been many cases of people finding odd objects in their packaged foods but this is a first. Apparently, this OP found a blue disc in a packet of sour cream crisps with the words “ferrous 25mm BST, cert number 213026B” on it. Needless to say, they were completely baffled but thankfully, the internet had answers.
Turns out this is a “testing chip” that goes through metal detectors to make sure that they’re working. In this case, the test had ironically failed since a foreign object ended up in a chips packet. Calling this in would definitely get someone in trouble!