I would say that your experience suggests you are in the UK, not the opposite. In "the old days" milk, cream, etc. used to go sour at the end of their normal shelf life. They still do elsewhere but not any more in the UK, it goes bitter exactly as you describe it. Sour milk and cream are quite useful in a number of culinary applications, now you have to buy "soured" milk and cream for those purposes as fresh products/leftovers cannot ultimately be used that way.
I have tried to find out why this is and wrote to the Dairy Council asking for an explanation - no response at all. That you have this in yogurt is something new to me, I have never heard of this (I don't eat the stuff nor does anyone in my household) and it is the first direct suggestion/evidence of undeclared chemicals being used in the production/process and one that indirectly suggests that something similar may be used when processing fresh milk and cream. This is bad news for me as I drink copious quantities of milk and we use quite a lot of cream in/on our food. I don't know what I/anyone can do to establish what is going on but meanwhile I shall remain very suspicious of UK dairy products.