Brexit is done, with obvious political impact on Britain. The political impact can be classified to internal and external effects; on the internal side, Brexit affects the political relations between legislative and executive within UK. On the other side, Brexit has effects on the UK's relations with European Union EU. Among other things, this paper focuses on the Brexit's impact on the Northern Ireland and its relations with EU and The Republic of Ireland, the issue of borders and the constitutional situation of Northern Ireland. In addition to the case of immigration in Britain which constitute several political and cultural issues within UK.