UK, Ireland / Buying a Polish vehicle in the UK [28]

Hi guys.
is there any one who could help please I have very complicated case. I live in UK, I have British passport and I am also Croatian with Croatian passport. I have friends from Poland in UK who is willing to give me they car for free on Polish plates, car is insured. That car I would like to transfer to Croatia and register that car on Croatian plates. How I should do that, please let me know how much you know as I think that my case is very rear so what ever you know every information is helpful. Many thanks.