Every single expat I have ever spoken to in years of living here says the same thing so it is not just my perception.
I must honestly say that every single Polish "expat" or guest worker or whatever you wish to call them "says the same thing so it is not just my perception" (about perceived "British rudeness").
May I present the theory that it is not so much a question of levels
of rudeness, but rather different areas
in which the respective "national" rudeness(es) show themselves? And because these areas obviously don't overlap, they tend to shock and anger the outsider, no matter how long they may have lived in the other country.
Believe me, my mother was Czech, my father is Polish, and though they were married for over 20 years, things would come up every day leading to heated discussions at least - and these were little, tiny, negligible things to start with, just different
in the Czech and Polish cultures/societies. Even issues like choosing or not choosing a specific term, name, gesture! They would get miffed and sulk for hours! Now remember how close these two cultures obviously are, at least to the non-Slav. ;-)
In the context of this, think of the differences between Poland and Britain, Greece and France, Britain and Finland...