As for the first time in a generation there is more than a serious prospect of a member state leaving the European Union, in this thesis I am going to investigate the situation where the United Kingdom withdraws its membership of the European Union, taking into consideration the economic consequences of this as well. The importance of the study comes from the perspective of the fact that if the United Kingdom leaves the European Union the impact would depend on the new relationship between the United Kingdom and the European Union. A lack of clarity over what would happen within the European Union is just one reason why this subject has to be treated, anyway the process will belong and uncertain, taking ten years or more.