You don't understand. It's literally just a reference to full-fat and semi-skimmed milk, like a small joke. It's OK to not understand, you're not from the UK, but it's a bit outlandish to turn your own failure to understand a very basic joke into grand claims about British education lol.
I think you've just been living in the UK too long and should probably go home. You sound completely depressed. 20 years in a country you hate populated by people you despise sounds like Hell. It's not too late to make a change. Where's home for you then?