Residency for tax purposes
It's important to determine whether you are Polish or UK resident because that will determine where your taxes are due and whose health insurance system you fall under. The rule of thumb is that if you are in an EU country for 6 months or more then you are resident there.
If you are UK resident then:
* you continue to pay your taxes in the UK
* you pay national insurance in the UK
* you can get a European Health Insurance Card from the NHS to cover medical bills in Poland
If you are resident in Poland then:
* you will now fall under the Polish tax system. The tax bands are lower than those in the UK and your GLOBAL INCOME is taxable, NOT JUST MONEY YOU EARN IN POLAND!
* you will pay social insurance to ZUS
* ZUS can give you a European Health Insurance Card which you should use when you are back in the UK
What happens if I move to Poland?
In theory when you decide you are 'resident' in Poland you should inform the authorities accordingly. That means you tell the Inland Revenue you have left the UK and they will calculate whether they owe you any tax back or not. If you start working for a Polish company then they will sort out your tax and ZUS for you. If you were self-employed in the UK then you need to talk to an accountant. You may decide to open a new Polish company, or you may decide to register your UK company as an employer in Poland so that it can pay social insurance for you.
What happens if I work in the UK during the week but return to Poland at the weekends?
In situations such as this it comes down to defining your 'place of living'. If you stay in hotels during the week but your house is in Poland that's one point for Poland. If your family (spouse, kids etc..) live in Poland that's another point for Poland. If you spend your spare time in Poland, again that counts as living in Poland. If you think your situation is arguable then you can ask the Polish tax office (Urząd Skarbowy) to make a ruling. An application for a ruling is free of charge. You describe your situation and put your point of view in it. They have 3 months to rule. If they don't rule within this time then your point of view prevails and is binding for all tax offices in Poland.
What happens if I don't become resident in Poland?
Probably nothing for a while. But you might get a knock on the door one day from the tax office. You run the risk that they will rule you as a Polish resident and give you a backdated tax bill for your global income. Having said that, Poland has tax agreements with most countries so that you are not charged twice for tax. But I don't know if there are any penalties involved or if there would be a tax bill still due to differences in tax bands etc.. If this has happend to anyone I would be keen to hear about it!