What really surprised me was the core principle at British unversities - "don't assume prior knowledge of anything". It basically meant that on a CS course, they teach you basic level maths, basic programming skills, you spend the entire 1st year of university learning what we learnt in school around age 15-16. A Polish university absolutely won't be teaching you basic algebra,statistics or core concepts of programing on a CS course - you are simply required to know these things, otherwise wtf are you doing on a CS course.
Also in general, I find the elective system of subjects in British schools to be.....poor. As in, I was(and am) surrounded by perfectly normal adults who are good in certain subjects(the ones they picked) and who have zero knowledge in others(the ones they didn't pick). I feel like my own Polish education has given me a very broad understanding of a lot of different subjects even if I wasn't personally interested in them. Like, even though I went to a school with a "maths and CS focus"(which just meant these two subjects had 2x the number of lessons each week), we still had lessons in history, physics, chemistry, biology, Polish literature.....all of it was mandatory, you couldn't just decide to skip it. At the time, I thought it was useless, but in hindsight I am very grateful for it because it has given me at least basic level of knowledge in many different subjects, whereas my British peers just can't even have a conversation about basic chemistry for instance, since they never took it as a subject.