The United Kingdom's withdrawal from the European Union launched a transformation of the Euro-Atlantic security area, which led to uncertainty and the creation of political forks for key regional actors on military integration. The Euro-Atlantic security complex has moved towards bipolarity with centers in NATO and the EU, but so far this is only a trend. The consequence of Brexit is the strengthening of polycentricity in the European sub-complex of the Euro-Atlantic security area and the strengthening of the leadership of the EU, Paris and London. The future system and structure of this sub-complex largely depends on the results of negotiations between the UK and the EU both on trade and economic issues, and on cooperation in the field of security, defence and foreign policy cooperation. The economic aspects of Brexit are still not clear, the economic losses due to the coronavirus pandemic and the slowdown in the global economy are obvious, which leads to unpredictability in the formation of military and foreign policy budgets of both the UK and the EU member states. The UK intends to establish the most deep and comprehensive military-political cooperation with the EU. In the absence of institutional mechanisms for the interaction of Brussels with London on security issues, the country seeks to strengthen bilateral ties in the field of foreign policy, security and defence with EU leaders, primarily France and Germany. An important influence on the above processes have external actors, among them the United States play a paramount role. The UK is likely to seek its place between the USA and the EU, which will force London to deliberately combine multilateral and bilateral cooperation with individual countries. The security area in Europe will gain more certainty after the conclusion of a political agreement between the UK and the EU, but this will not happen until the conclusion of a trade and economic agreement.