The Britons' referendum of 23 June 2016, known as Brexit has led to the UK’s withdrawal from the European Union (EU). Within the context of ontological security theory, Brexit can be seen as a campaign by British people and politicians who have never been willing to see their country which was once at the center of world politics, in an alliance with 27 different European countries. For Britons, the EU is a federation aimed at  regional integration of sovereignty and foreign policy of the member states, and consequently it might limit the ability of British government to conduct an independent foreign policy. Half a century of British membership in the EU and its recent withdrawal have raised doubts about the Kingdom’s post-Brexit foreign policy. The potential for changes in the three key principles of British foreign policy (i.e., the Anglo-American special relationship, responsibility to protect, and multilateralism) are at the top of the ambiguities in the post-Brexit British foreign policy. In the research hypothesis, it is argued that Brexit  will have a positive impact on the US-British special relationship, but it will create a more limited space for the use of British economic and military capabilities based on the principle of protection responsibility,, and it will  lead Britain to upholding the principle of multilateralism by seeking alliances that unlike its membership in the EU will not undermine its institution of sovereignty and independent foreign policy.
In this paper, the authors use a descriptive-analytical approach and a multi-case study method to analyze the impact of Brexit on these three principles. By using this method, an attempt is made to examine these three key principles on a case-by-case basis and analyze the effect of Brexit on them separately. A key objective is to scrutinize the attitudes and preferred policies of the two British major parties (i.e., Conservative Party and Labour Party) concerning these principles and the expected impact of Brexit on them. For the theoretical framework of the present study, the theory of ontological security is selected. An important theoretical assumption is that the identity of a state is not necessarily formed only by an external factor, as an ‘other’. Identity is also constructed through the development of autobiographical narratives that rely on a state’s history and experience, which bring about the continuity of the state's existence and its perception of self-identity and its raison d'être. Through these narratives, the individuals in the state and society recognize who they are and how they should act in international politics.
In connection with the Anglo-American special relationship, concepts such as Anglo-Saxonism and Englishness have become powerful narratives that have historically strengthened British-American bonds. Regarding the responsibility to protect, the two main British parties, especially the Conservatives, fully endorse this principle. In this sense, one of the main narratives among British politicians has been the Kingdom’s glorious past in defense of democratic values. They view their country as committed to promoting human freedoms, democracy, and anti-terrorism activities, which they call liberal interventionism. Furthermore, one of the characteristics of British foreign policy over the centuries has been the independence of its foreign policy. With the growing integration of the EU, the independence of British foreign policy as a dominant autobiographical narrative has been threatened. After the Britain’s withdrawal from the EU, the British politicians need to establish an efficient multilateral system, to redefine the country’s raison d'être and to create alternative narratives that justify their behaviour and actions, especially in the face of challenges from the emerging powers. Concerning these ontological issues, some scholars argue that the presence of a major power such as Britain in the EU as a tight alliance has been confronted with challenges from the beginning. In other words, it is far-fetched for a country like Britain, once at the top of the international power structure to merge its national sovereignty and foreign policy independence into a quasi-federation like the EU, and acquire no exceptional superiority over other members. However, the withdrawal from the EU in which Britain has been a key member state for half a century will undoubtedly change the main principles of British foreign policy (Anglo-American special relationship, responsibility to protect, and multilateralism). Our findings are summarized as follows:
After Brexit, the capacity to safeguard the special relationship will depend on Britain's willingness and ability to resolve US suspicions. In connection with the Britons’ intentions to maintain and strengthen the special relationship, the two factors of mutual guarantee of the relationship and the approval and acceptance of a lesser role by Britain will be essential. However, the type and extent of bilateral assurances, particularly from the UK will help the Kingdom to reaffirm its commitment to US policies. Concerning the issue of British less significant role in the special relationship, it is clear that the US expects to play the dominant role and its policy of giving a secondary and subordinate role to Britain will be pursued more prominently in post-Brexit foreign policy. Regarding the responsibility to protect, there are many concerns in post-Brexit Britain, and most of them are due to the fact that Britain will be in a weaker position, both economically and militarily. Therefore, many in Britain believe that intervention to fulfill their country’s responsibilities, especially in the form of military intervention, even for humanitarian purposes, should be the last resort. Others believe that Britain will increasingly have to rely on its soft power capacities to fulfill its responsibility to support liberal interventionism. Finally, with regard to the third principle, it should be noted that due to its inability to pursue a unilateral foreign policy in the post-Brexit period, the UK is likely to continue to pursue the policy of multilateralism in its foreign policy, and to participate in coalitions that do not limit British national sovereignty and foreign policy independence, as shown in the case of NATO. The present study helps identify the challenges and opportunities that the phenomenon of Brexit has created for the key principles of British foreign policy and better evaluate its foreign policy behaviors in the post-Brexit period.