no way, they bulid everyting on that, no science, no secular society. they based everything on ridiculous believes
You are quite mistaken. The current and immediate past situation in Northern Ireland has little to do with religion, it is more related to the political aspirations of Unionists and Nationalists (google each term - there's a vast amount of info available on them) and to previous discriminations of Unionists against Nationalists.
Everyone's at peace now, so there should certainly be no problems for a Polish person in Northern Ireland, regardless of religion.
Of course there's always the looney fringe who want trouble, but you get those in every country - they're all the same, but with different excuxes.