Yes it is possible for him to give a power of attorney to a local Pole that he trusts but the notary dealing with that will probably take a lot of steps to ensure it is a kosher POA (including British notarization, official translation etc and I'm not sure about Britain but in some countries would also need to be apostilled - a kind of stamp saying that the notary is a notary).
All of that would add up to a few hundred quid of cost so if your partner has some spare time it might be as well to use Ryanair and have a short holiday in Poland and take care of it "na cztery oczy"
So, in other words you actually mean that you wish to sell the house? If so, then you might want to have the house inspected and evaluated (appraised) based on what the condition of the house is like. The other choice is if the house is sitting empty, you can rent it.