The paper focuses on the very topical issue of conclusion of the membership of the State, namely the United Kingdom, in European integration structures. The question of termination of membership in European Communities and European Union has not been tackled for a long time in the sources of European law. With the adoption of the Treaty of Lisbon (2009), the institute of 'unilateral' withdrawal was introduced. It´s worth to say that exit clause was intended as symbolic in its nature, in fact underlining the status of Member States as sovereign entities. That is why this institute is very general and the legal regulation of the exercise of withdrawal contains many gaps. One of them is a question of absolute or relative nature of exiting from integration structures. Today’s “exit clause” (Art. 50 of Treaty on European Union) regulates only the termination of membership in the European Union and is silent on the impact of such a step on membership in the European Atomic Energy Community. The presented paper offers an analysis of different variations of the interpretation and solution of the problem. It´s based on the independent solution thesis and therefore rejects an automatism approach. The paper and topic is important and original especially because in the multitude of scholarly writings devoted to Brexit questions, vast majority of them deals with institutional questions, the interpretation of Art. 50 of Treaty on European Union; the constitutional matters at national UK level; future relation between EU and UK and political bargaining behind such as all that. The question of impact on withdrawal on Euratom membership is somehow underrepresented. Present paper attempts to fill this gap and accelerate the scholarly debate on this matter globally, because all consequences of Brexit already have and will definitely give rise to more world-wide effects.