The article presents the results of a study on the historical role and special aspects of Great Britain's participation in the formation and implementation process of the European Union Common Foreign and Security Policy. The study demonstrates the transformation of the British Government's position on the EU's CFSP and on the Common Security and Defense Policy as its component. Also, the article reviewed the influence of US-British and German- French relations on Britain's participation in the EU's CFSP. The paper presents the historical aspects of the country's practical involvement in the CFSP implementation, in particular, in the enlargement policy and in the EU's Eastern European policy (first of all, the policy towards Ukraine). Among few pioneering studies in Ukrainian historiography, this paper analyzes the impact of the Brexit process on the United Kingdom's involvement in the EU's CFSP and European integration in general since the referendum on 23 June 2016. The study concluded that the EU's CFSP opportunities attracted the British government, but its deeper participation in the integration processes was prevented due to the established principles and directions of the country's foreign policy. The state government at various times has ignored the objective opportunities for its leading position in the EU in the field of foreign and security policy. In general, Great Britain failed to find its place in the European Union, which resulted in the Brexit process and the country's withdrawal from the European Union.
