/ Is it common for Polish people to speak English in Poland?
Rather not. Few people over 40 speak it at all, even among the well educated.
You seem to be putting the bar at far too high a level.
I personally know a great many people over forty who speak English (imho) well.
Furthermore, I'd suggest far more than 20% of students can speak English well enough to have more than a 'basic' conversation.
It depends how you define 'basic'.
I'm not aware of Poles having a 'terror' of reading English. Probably most Brits and Americans don't read literature for pleasure even in their own language, let alone anyone else's. And if they do, 99% would read in the translation rather than the original.
Given that it is obviously far more difficult to communicate in a second language than in your own, I'd say Poles are (generally) doing pretty well at English.