My partner and I have written wills in the UK leaving each other most of our estates when one of us dies. I am British and he is Polish, (with permanent residence granted before Poland entered the EU). Incidentally, we are not married or in a civil partnership.
QUESTION : Can the intention of these wills be overridden by Polish law?
As you are not married, the remaining partner will not be entitled to the tax-free inheritance allowance and will have to pay tax on the estate, which will be considerable. Consult a solicitor immediately.
As a lawyer, I would also add the following: it would be better for you to write a will ALSO in Polish according to the rules of Polish inheritance law. If there is some property or real esate in Poland, only Polish courts will have jurisdiction over this real estate. Even if you have a will in Polish and English, some Polish members of your partner's family may be entitled to receive "zachowek'.