i think her ex is a abusive alcoholic, woman beater after a drink.
None of that matters to the Polish family court, none of it. I know a family where the father has multiple convictions for violence against both his ex-wife and son but the court still forces his daughter to spend time with him. And that is a case which doesn't involve a foreigner or a Pole who has left Poland. Things which in the UK would most certainly result in prison sentences are simply ignored by the family court here. I worked with a woman who divorced her husband due to him having the habit of getting drunk and kicking the crap out of her. The court decided that the break-up of the marriage was due to faults on both sides and as a result she is now paying him alimony as he drinks too much to hold down a job (of course he still works cash in hand without telling the court). BTW, if your Mrs' ex decides to pull a similar trick, the Polish court will take into account your income when assessing how much to give him. I know another case about child support payments where a man submitted income statements to the family court showing that he earned less than he had been paying every month in child support (to the mothers of his three children) for the past three years. The court accepted those documents as being accurate. If you get involved in the family courts here, anything can happen. And as a foreigner, you'll get the shiitty end of the stick nine times out of ten.
if my partners son goes back to poland it will only be for breif visits to see grandad and grandma.
Even if those grandparents are her parents, I'd strongly recommend that they come to UK. If the ex-husband gets his hands on the kid in Poland, you face a real battle to get the kid back. As for the ex-husband's parents, don't even let them know where the kid lives.