You are registered in the UK, but you say that you livwe in Poland?
To register on ebay.co.uk you have to provide a verified address in the UK. Otherwise, you may need to register in Poland.
Either way, if you or the items you sell are located in Poland VAT may be payable, which eBay would collect on behalf of HMRC.
You will also need to think about an address for returns. If a buyer complains that an item is not as described you may be required to arrange and pay for it to be returned to Poland.
