UK isn't an outlier for Central Europe, because speeds are universally pretty bad there (Germany, France, Spain, Poland, Italy etc. all have similarly bad or even worse results). Sure, it's not Russia-bad or Australia-bad, but it really ain't good.
https://www.fastmetrics.com/internet-connection-speed-by-cou... https://www.speedtest.net/global-index
In both of these Poland ranks similarly badly (31st/43rd) despite entirely different data sources. France ranks slightly better but still pretty bad. Note that the first site lists median speeds, while speedtest.net shows averages.