Actually Apples and Cheese go together very well! You should know that particularly since you live Germany.
So what about divers who "learned" when there were no schools to teach them? Are there in fact any schools out there that teach "round the world" diving? I rather doubt it.
But then I do believe that most diving schools, including the BSAC ones, teach the rudiments of diving and then throw the hapless student out into the real world (as do the schools and universities etc) and that student either does, or does not, become a real diver.
Me? I first became a diver in '57 (I think) and I'm still learning.
As for British divers being better than all others (I've not dived, nor am I ever likely to, in British waters) that's a load of oLd cobblers. Diving depends on the conditions of the day, the water to be dived in and a host of other things I couldn't be bothered with ATM, but, whatever one does, if in ANY doubt can the dive.