Upvote:3
There are two different issues here:
- Not breaking the law.
An UK/Polish dual citizen can stay in the EU without time limit. (There are rules how other EU states can deny entry, but they have nothing to do with overstaying. Threats to public order or public health, for example.)
- Not giving the appearance of having broken the law.
An UK/Polish dual citizen who travels on the UK passport and stays longer than permitted for an UK citizen has given the appearance of an overstay. That can be resolved by showing the Polish citizenship e.g. by presenting the Polish passport, but that passport might not be readily available in the scenario described here.
Entering on one passport and leaving on another gives confused documentation.
Again, not illegal at all, but it might raise questions which have to be answered by showing the other document as well.
So the easy option is to enter the EU on the EU passport and the UK on the UK passport at all times. The other option is legal as well, but it might cost time later on.
Upvote:10
No, if you are a Polish citizen, you can stay in Poland for as long as you want. Having ever been or lived there before, other citizenships, where you reside now, the purpose of your trip, your financial situation, even actually holding the passport (the document) do not change that.